JP3608985B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device used for a light source or the like of an optical disk system and a manufacturing method thereof, and more particularly to a window structure semiconductor laser device excellent in characteristics of high output operation and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, in order to improve the writing speed in writing information to an optical disk typified by CD-R / RW and DVD-R / RW, a semiconductor laser having an optical output exceeding 100 mW is expected to appear. The challenge for increasing the output of a semiconductor laser and ensuring its reliability is to suppress the degradation of the end face and to realize a low current. In response to these problems, the active layer is a quantum well and the quantum well active layer near the end face is disordered. A window structure semiconductor laser has been proposed. This is because end face destruction due to so-called COD (Catastrophic Optical Damage) occurs only by protecting the end face of the resonator with a conventional dielectric film, and it is impossible to obtain good high output characteristics. In order to improve the laser light output level at which COD occurs, a semiconductor laser element capable of high output operation can be realized by making the resonator end face a window structure and eliminating light absorption at the end face. As a prior art of a semiconductor laser having such a window structure, the structure of a semiconductor laser device described in Japanese Patent Laid-Open No. 9-23037 is shown in FIG.
[0003]
10A is a perspective view including the light emitting end face, and FIG. 10B is a cross-sectional view of the waveguide taken along line Ia-Ia in FIG. 10A, that is, a cross section in a direction parallel to the traveling direction of the laser light. FIG. Further, (c) is a cross-sectional view in the layer thickness direction along the line Ib-Ib in (a), that is, a view perpendicular to the traveling direction of the laser beam. In FIG. 10, 1001 is a GaAs substrate, 1002 is an n-type AlGaAs lower cladding layer, 1003 is a quantum well active layer, 1004a is a p-type AlGaAs first upper cladding layer, 1004b is a p-type AlGaAs second upper cladding layer, and 1005 is p Type GaAs contact layer, 1006 (shaded portion) is a hole diffusion region, 1007 (shaded portion) is a proton injection region, 1008 is an n-side electrode, 1009 is a p-side electrode, 1020 laser cavity end face, and 1003a is a quantum well active layer Reference numeral 1003b denotes a window structure region formed in the vicinity of the laser resonator end face 1020 of the quantum well active layer 1003.
[0004]
Next, a conventional method for manufacturing a semiconductor laser device will be described with reference to a process diagram shown in FIG.
[0005]
An n-type AlGaAs lower cladding layer 1002, a quantum well active layer 1003, and a p-type AlGaAs first upper cladding layer 1004a are sequentially epitaxially grown on an n-type GaAs substrate 1001 (FIG. 11A). Next, on the surface of the p-type AlGaAs first upper cladding layer 1004a, SiO₂A film 1010 is formed, and a stripe-shaped opening 1010a extending in the direction of the laser resonator is formed with a length that does not reach the end face of the laser resonator (FIG. 11B). Next, when this wafer is thermally annealed at a temperature of 800 ° C. or higher in an As atmosphere, SiO 2₂Ga atoms are sucked up from the surface of the p-type AlGaAs first upper cladding layer 1004a with which the film 1010 is in contact, and Ga vacancies are generated in the p-type AlGaAs first upper cladding layer 1004a. Diffusion until reaching 1003, the quantum well layer structure is disordered. In the disordered active layer region, the effective forbidden band width is widened, so that it functions as a window transparent to the oscillation laser beam.
[0006]
Furthermore, SiO₂The film 1010 is removed, and a p-type AlGaAs second upper cladding layer 1004b and a p-type GaAs contact layer 1005 are sequentially epitaxially grown on the p-type AlGaAs first upper cladding layer 1004a. (FIG. 11 (c)). Next, a resist film is formed on the p-type GaAs contact layer 1005, and the SiO film is formed by photolithography.₂A stripe-shaped resist 1011 is formed in the same region as the stripe-shaped opening 1010 a of the film 1010. Next, proton implantation is performed from the surface side of the p-type GaAs contact layer 1005 using the striped resist 1011 as a mask to form a high resistance region 1007 to be a current blocking layer (FIG. 11D). Finally, an n-side electrode 1008 is formed on the GaAs substrate 1001 side, and a p-side electrode 1009 is formed on the p-type GaAs contact layer 1005, and the wafer is cleaved to obtain the semiconductor laser device of FIG. The conventional semiconductor laser device described above can achieve high output characteristics inherent in a semiconductor laser device having a window structure as compared with a method of disordering a quantum well structure by ion implantation and diffusion of the ions, and at a COD level. It is described in the publication that it has high reliability and high reliability.
[0007]
[Problems to be solved by the invention]
However, in the conventional method of manufacturing a semiconductor laser device, after forming the window structure region, SiO having an opening is formed.₂Since the film is removed, it is difficult to distinguish the boundary between the window structure region in which the quantum well layer is disordered and the active region in which the quantum well layer is not disordered. Therefore, when forming the current block region, it is necessary to strictly align the stripe-shaped resist region serving as the proton implantation mask and the active region, so a marking process and alignment process are newly added for alignment. Must be added. If the active region reaches the laser cavity end face, or if the window structure region and the proton injection region shift, the reliability and various characteristics of the laser element deteriorate, so the above alignment requires high accuracy. There were problems of cost increase and yield decrease due to increased man-hours.
[0008]
Furthermore, in the conventional method of manufacturing a semiconductor laser device, SiO₂Since the film is formed on the AlGaAs layer or the GaAs protective layer of 100 Å or less, even if there is a GaAs protective layer of 100 Å or less, Al reacts preferentially over the thin GaAs layer, and the target SiO₂This hinders the process of sucking up Ga atoms. As a result, the generation of Ga vacancies due to Ga suction is insufficient, and SiO₂There is a problem that the reaction to increase the band gap of the quantum well layer directly below becomes insufficient and the function as a window cannot be exhibited. In addition, the SiO₂By the reaction of Al with Al₂There was also a problem that it was difficult to remove.
[0009]
The object of the present invention is to provide SiO₂The window region in the vicinity of the end face can be efficiently formed without hindering Ga suction, and the current non-injection region can be formed in a self-aligned manner with no particular alignment with the window region. It is to provide a window structure semiconductor laser device excellent in controllability and reliability and a method for manufacturing the same, and to improve yield and reduce cost.
[0010]
[Means for Solving the Problems]
The present invention has been made to achieve the above object, and a semiconductor laser device according to the present invention includes a first conductivity type first cladding layer, a quantum well active layer, a first conductivity type substrate, A second conductivity type second cladding layer, a second conductivity type third cladding layer comprising ridge stripes in the direction of the resonator, and a first conductivity type current configured to embed ridge stripe side surfaces of the third cladding layer A block layer and a cap layer of the second conductivity type formed on the third cladding layer, a dielectric film formed in a direction perpendicular to the ridge stripe in the vicinity of the resonator end face on the cap layer, and the dielectric layer The band gap of the quantum well active layer directly under the body film is larger than the band gap of the quantum well active layer inside the resonatorIn addition, a second conductivity type contact layer is provided on the cap layer in a region where the dielectric film is not formed.The configuration.
[0011]
By doing so, the dielectric film near the resonator end face prevents current injection into the window region where the band gap of the quantum well active layer is large, so that the reactive current is reduced and the semiconductor has excellent high output characteristics and reliability. A laser element is obtained. Furthermore, since the end face window formation and the current non-injection region formation can be formed by self-alignment, it is excellent in mass productivity and can realize cost reduction by improving yield.
[0012]
[0013]
Also,By doing so, a window region having a large band gap of the quantum well active layer can be easily confirmed even after the contact layer is formed, and the cleavage process for forming the resonator is facilitated, so that mass production is excellent and the yield is also improved. .
[0014]
Preferably, a second conductivity type contact layer is formed in both the region of the cap layer where the dielectric film is formed and the region where the dielectric film is not formed, and the dielectric film of the contact layer is A step or a morphological difference is provided between a portion formed on the formed region and a portion formed on the region where the dielectric film is not formed.
[0015]
As a result, there is a difference in level difference or morphology between the portion of the contact layer formed on the region where the dielectric film is formed and the portion formed on the region where the dielectric film is not formed. The window region can be identified by the presence of the second conductive type contact layer in both the cap layer region where the dielectric film is formed and the region where the dielectric film is not formed. Since the semiconductor laser device can be mounted upside down and heat dissipation can be promoted, the temperature characteristics of the device can be improved.
[0016]
Preferably, the difference Δλ between the band gap wavelength λw of the quantum well active layer immediately below the dielectric film and the band gap wavelength λa of the quantum well active layer inside the resonator is in the range of 10 nm ≦ Δλ = λa−λw ≦ 50 nm. And
[0017]
Then, the decrease in COD level due to an increase in light absorption at the light exit end face when Δλ = λa−λw is less than 10 nm, and an increase in crystal defects near the end face when Δλ = λa−λw is 50 nm or more and the accompanying non-conformity. A function as a window structure can be secured by preventing a decrease in COD level due to an increase in the number of light emitting centers.
[0018]
Preferably, the cap layer of the second conductivity type is Al._xGa_1-xIt is assumed that As (x ≦ 0.1).
[0019]
By doing so, Al containing a large amount of Al on the surface on which the dielectric film is formed_xGa_1-xEven in the case of As (x> 0.1), it is possible to prevent the generation of Ga vacancies due to the inhibition of Ga absorption by Al and to promote the reaction that effectively increases the band gap of the quantum well active layer. .
[0020]
Preferably, the thickness of the cap layer of the second conductivity type is in the range of 100 nm to 1000 nm.
[0021]
By doing so, suppression of the generation of Ga vacancies due to inhibition of Ga suction due to diffusion from the third cladding layer to the Al dielectric film when the film thickness of the second conductivity type cap layer is less than 100 nm, and Due to the fact that the thermal annealing conditions for increasing the band gap of the quantum well layer by increasing the distance from the dielectric film to the quantum well layer when the thickness of the cap layer is 1000 nm or more must be performed at a higher temperature for a longer time. Deterioration of device characteristics due to diffusion of a dopant present in the crystal can be prevented, and a reaction for increasing the band gap of the quantum well active layer can be promoted.
[0022]
Preferably, the dielectric film formed in the vicinity of the end face of the resonator is SiO. _x And
[0023]
By doing so, SiO _x Has a high function of absorbing Ga, and therefore can effectively promote a reaction that increases the band gap of the quantum well active layer.
[0024]
Preferably, the dielectric film has a thickness in the range of 100 nm to 1000 nm. If the thickness of the dielectric film is less than 100 nm, the effect of sucking up Ga is insufficient, and the amount of Ga vacancies for increasing the band gap of the quantum well active layer is insufficient. On the other hand, when the film thickness of the dielectric film exceeds 1000 nm, cracks are generated in the dielectric film during thermal annealing, and the thermal stress is released, thereby inhibiting the diffusion of Ga vacancies.
[0025]
Accordingly, the band gap of the quantum well active layer can be increased to the extent that the function as the window structure can be sufficiently exerted by setting the film thickness within the above range.
[0026]
Preferably, the length of the region where the band gap of the quantum well active layer in the vicinity of the end face of the resonator is larger than the band gap of the quantum well active layer inside the resonator is 10 μm or more and 60 μm or less.
[0027]
By doing so, it is possible to suppress the leakage current to the end face and prevent the efficiency of the element from being reduced due to free carrier loss.
[0028]
Further, on the first conductivity type substrate, the first conductivity type first cladding layer, the quantum well active layer, the second conductivity type second cladding layer, the second conductivity type etching stop layer, the second conductivity type second cladding layer. A step of sequentially epitaxially growing a third cladding layer and a second conductivity type cap layer, and a step of processing the second conductivity type third cladding layer and the second conductivity type cap layer into a ridge shape in a stripe shape in a resonator direction; Burying a side surface of the ridge with a first conductivity type current blocking layer, removing an unnecessary layer formed simultaneously on the ridge at the time of burying the current blocking layer, and planarizing the surface, and stripes of the ridge Forming the dielectric film in a direction orthogonal to the direction of the direction, and the band gap of the quantum well active layer immediately below the dielectric film by thermal annealing is equal to the band gap of the quantum well active layer inside the resonator. A step of forming a second conductivity type contact layer while leaving the dielectric film, and a light emitting end face disposed in the region of the quantum well active layer having a larger band gap than the inside of the resonator. Forming a resonator to do so.
[0029]
By doing so, the dielectric film has the role of preventing current injection into the window region of the quantum well active layer where the band gap of the quantum well is increased, and the end face window formation and the current non-injection region formation are realized by self-alignment. Therefore, it is not necessary to align the window region and the non-injection region, and the process can be simplified.
[0030]
Preferably, in the step of forming the dielectric film, a resist pattern having an opening is formed, the dielectric film is formed on the entire surface, and then the dielectric film formed on the resist is lifted off.
[0031]
If the dielectric film is formed by lift-off, since there is a resist in the region other than the window, plasma damage is not caused when the dielectric film is formed. Therefore, the controllability for suppressing the band cap expansion of the quantum well active layer in the region other than the window and selectively increasing the band gap only in the window region is improved. In addition, a window structure forming process can be provided without deteriorating the crystallinity of regions other than the window.
[0032]
Preferably, the dielectric film is formed by either sputtering or plasma CVD.
[0033]
If the dielectric film is formed by either a sputtering method or a plasma CVD method, a point defect due to plasma damage is newly generated on the surface simultaneously with the formation of the dielectric film, and diffusion of Ga vacancies can be further promoted. An effective window region can be formed.
[0034]
The conditions for forming the dielectric film for enlarging the band gap of the quantum well active layer immediately below the dielectric film by plasma CVD are as follows: RF power is 100 W or more, substrate temperature is 250 ° C. to 350 ° C. It is good to do. The thickness of the dielectric film is 100 nm or more and less than 1000 nm.
[0035]
By making the RF power 100 W or more, it is possible to more effectively generate point defects due to plasma damage on the surface and promote the diffusion of Ga vacancies on the other hand, while the substrate temperature is set to 250 ° C. to 350 ° C. And the adhesion of the dielectric film can be maintained. By setting the thickness of the dielectric film to 100 nm or more and less than 1000 nm, the band gap of the quantum well active layer can be increased to such an extent that the function as the window structure can be sufficiently exhibited.
[0036]
As conditions for forming the dielectric film for increasing the band gap of the quantum well active layer immediately below the dielectric film by sputtering, the RF power is 200 W or more, the substrate temperature is 250 ° C. to 350 ° C., The dielectric formation film thickness is 100 nm or more and less than 1000 nm.
[0037]
By setting the RF power to 200 W or more, point defects due to plasma damage can be more effectively generated on the surface, and further diffusion of Ga vacancies can be promoted. Further, the adhesiveness between the cap layer and the dielectric film can be maintained by setting the substrate temperature to 250 ° C. to 350 ° C. Furthermore, by setting the film thickness of the dielectric film to 100 nm or more and less than 1000 nm, the band gap of the quantum well active layer can be increased to such an extent that the function as the window structure can be sufficiently exhibited.
[0038]
Preferably, there is provided a step of cleaning the surface of the cap layer by performing reverse sputtering immediately before forming the dielectric film on the cap layer of the second conductivity type by sputtering.
[0039]
As a result, Ga SiO _x A natural oxide film formed on the cap layer that inhibits the absorption reaction into the cap layer can be effectively removed in-situ, and a point defect due to plasma damage is newly generated on the surface of the cap layer. Can promote pore diffusion.
[0040]
Preferably, in the step of forming the dielectric film on the cap layer of the second conductivity type by a sputtering method, a DC bias of 2 kV or more is applied to the wafer.
[0041]
As a result, SiO _x At the same time as the formation of, more point defects due to plasma damage are generated on the surface of the cap layer, and diffusion of Ga vacancies can be promoted.
[0042]
Preferably, the thermal annealing condition for making the band gap of the quantum well active layer in the region immediately below the dielectric film larger than the band gap of the quantum well active layer in the region inside the other resonator is a heating rate of 80 ° C. / Second or more, a processing temperature of 800 ° C. to 1000 ° C., and a processing time of 10 to 60 seconds.
[0043]
As a result, it is possible to realize window region formation that achieves both promotion of Ga vacancy diffusion and suppression of dopant diffusion inside the crystal and does not deteriorate the characteristics of the semiconductor laser device.
[0044]
Preferably, the thermal annealing is performed by heating with a lamp only from the first conductivity type substrate side, and the cap layer and the dielectric film which are epitaxial growth surfaces are in contact with another substrate.
[0045]
As a result, surface roughness due to As missing from the surface of the cap layer and a decrease in crystallinity can be prevented.
[0046]
Further, after the thermal annealing step, the surface of the first conductivity type substrate is buffed and smoothed. If the roughness of the morphology generated due to the loss of As from the surface of the first conductivity type substrate due to lamp heating is left without being buffed, the substrate surface of the resist or organic substance in the subsequent photolithography process becomes the surface of the substrate. Adhere to. Such deposits are difficult to remove in a normal cleaning process, and cause a failure in epitaxial growth and a decrease in crystallinity in the subsequent MOCVD growth process.
[0047]
Therefore, the controllability of the process is improved by buffing and smoothing the surface of the first conductivity type substrate after the thermal annealing step.,Good reproducibility can be obtained and the device yield can be improved.
[0048]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]
FIG. 1 is a sectional view showing the structure of an AlGaAs semiconductor laser element according to Embodiment 1 of the present invention. 1A is a perspective view including a light emitting end surface, FIG. 1B is a sectional view of a waveguide taken along the line Ia-Ia in FIG. 1A, and FIG. 1C is a layer thickness taken along the line Ib-Ib in FIG. It is sectional drawing of a direction. 1 is an n-type GaAs substrate, 2 is an n-type Al_0.5Ga_0.5As first cladding layer, 3 is Al_0.3Ga_0.7Non-doped quantum well active layer including As guide layer (8 nm thick Al_0.1Ga_0.92 As well layers and 5nm thick Al between them_0.35Ga_0.654) p-type Al_0.5Ga_0.5As second cladding layer, 5 is p-type etching stop layer, 6 is p-type Al_0.5Ga_0.5The As third cladding layer 7 is a p-type GaAs cap layer and constitutes a ridge 102 extending in a stripe shape in the resonator direction. 8 is an n-type Al formed so as to fill the side surface of the ridge 102._0.7Ga_0.3As current blocking layer, 9 is a p-type GaAs planarizing layer, 10 is a SiO formed in a stripe shape in a direction perpendicular to the ridge stripe _x A film, 11 is a p-type GaAs contact layer, 12 is a p-side electrode, and 13 is an n-side electrode. Reference numeral 14 denotes SiO in the quantum well active layer 3. _x In the region immediately below the film 10, the band gap is larger than the band gap of other regions of the quantum well active layer 3 inside the resonator.
[0049]
Next, a method for manufacturing the semiconductor laser element will be described with reference to FIG.
[0050]
n-type GaAs substrate 1 (carrier concentration 2 × 10¹⁸cm^-3) N-type Al by MOCVD_0.5Ga_0.5As first cladding layer 2 (carrier concentration 8 × 10¹⁷cm^-3, Thickness 2 μm setting), undoped quantum well active layer 3 including guide layer, p-type Al_0.5Ga_0.5As second cladding layer 4 (carrier concentration 1 × 10¹⁸cm^-3, Thickness 0.2 μm setting), p-type etching stop layer 5, p-type Al_0.5Ga_0.5As third cladding layer 6 (carrier concentration 2 × 10¹⁸cm^-3, Thickness 1.1 μm), p-type GaAs cap layer 7 (3 × 10¹⁸cm^-3And a thickness of 0.7 μm) are epitaxially grown (FIG. 2A). Thereafter, a striped resist mask 101 is formed on the p-type GaAs layer 7 using a known photolithography technique, and the p-type GaAs layer is reached so as to reach the p-type etching stop layer 5 using a known etching technique. 7 and p-type Al_0.5Ga_0.5The As third cladding layer 6 is processed into a stripe-shaped ridge 102 having a width of about 3 μm (FIG. 2B).
[0051]
Next, by the second MOCVD method, the p-type GaAs layer 7 and the p-type Al_0.5Ga_0.5The side surface of the ridge 102 comprising the second cladding layer 6 on As is n-type Al._0.7Ga_0.3As block layer 8 (carrier concentration 1 × 10¹⁸cm^-3Then, after embedding with the p-type GaAs planarizing layer 9 (FIG. 2 (c)), the unnecessary layer formed on the ridge 102 is selectively removed to planarize the surface (FIG. 2). (D)).
[0052]
Next, by a PECVD method and a photolithography method, a 40 μm wide SiO 2 stripe is formed in a direction perpendicular to the stripe direction of the ridge 102. _x A film (thickness 500 nm) 10 is formed. SiO by plasma CVD _x The film formation conditions were an RF power of 100 W, a substrate temperature of 280 ° C., and a film thickness of 500 nm. The stripe pitch was set to 800 μm, which is the same as the resonator length (FIG. 2 (e)).
[0053]
Next, the SiO _x The wafer on which the film is formed is thermally annealed, and at this time, rapid thermal annealing is performed.
[0054]
FIG. 3 is a sectional view of an annealing apparatus for performing capless annealing by the RTA method. In FIG. 3, 301 is a wafer to be processed, 301a is an epitaxial growth surface (cap layer 7 surface), 301b is a substrate surface, 302 is a holding substrate, 303 is a lamp heater, 304 is a lamp heating window, and 305 is a pyrometer for temperature measurement. is there. As described above, the lamp heating from one side on the substrate 1 side and the epitaxial growth surface are performed in contact with the holding substrate 302 which is another substrate, thereby preventing surface roughness and crystallinity deterioration due to As missing from the cap layer 7 on the epitaxial growth surface. be able to.
[0055]
The thermal annealing conditions at this time were a temperature rising rate of 100 ° C./second, an annealing temperature of 950 ° C., and a holding time of 1 minute. If the rate of temperature rise is less than 80 ° C./sec, a rapid thermal stress for diffusing Ga vacancies to the quantum well layer is not applied, and a reaction for increasing a sufficient band gap does not occur. A heating rate is required. Furthermore, even if the annealing temperature is less than 800 ° C. and the holding time is 10 seconds or less, Ga vacancies cannot reach the quantum well layer sufficiently. On the other hand, when the temperature exceeds 1000 ° C. or when the holding time exceeds 60 seconds, diffusion occurs to the doping atoms inside the crystal, and the characteristics of the device are deteriorated. Therefore, the annealing conditions in the present embodiment need to be a temperature rising rate of 80 ° C./second or more, a processing temperature of 800 ° C. to 1000 ° C., and a processing time of 10 to 60 seconds, and more preferably, SiO by PECVD. _x Is formed, the diffusion rate of the doping atoms is suppressed and the band gap wavelength shift of the window region is suppressed by setting the temperature rising rate to 100 ° C./second or more, the processing temperature 860 ° C. to 960 ° C., and the processing time 30 to 60 seconds. can get.
[0056]
SiO by thermal annealing _x The band gap of the quantum well layer 14 in the region immediately below the film 10 is made larger than the band gap of other regions of the quantum well active layer 3 that is inside the resonator. In this thermal annealing, SiO _x Ga atoms from the surfaces of the p-type GaAs layer 7 and the p-type GaAs planarizing layer 9 immediately below the film 10 are SiO. _x It is sucked into the film 10 and Ga vacancies are generated inside the GaAs crystal. These Ga vacancies have a large diffusion constant and diffuse at a stretch toward the GaAs substrate 1 to increase the band gap of the quantum well active layer 14. SiO _x Has a high ability to absorb Ga, and SiO _x Directly under the film is GaAs that does not contain Al or In. Therefore, the reaction that effectively increases the band gap of the quantum well layer 14 can be promoted without hindering the reaction of sucking up Ga.
[0057]
Using a part of the wafer subjected to the thermal annealing by the RTA method, the microphotoluminescence (microPL) method is used to make SiO _x Quantum well layer directly under the film and othersTerritoryEach band gap of the quantum well layer in the region was measured. As is well known, the longer the photoluminescence peak wavelength, the smaller the band gap.
[0058]
FIG. 4 shows the measurement results of the microscopic PL. SiO _x The peak wavelength of photoluminescence from the quantum well layer directly under the film is SiO 2 _x It can be seen that the wavelength is shifted to the shorter wavelength side by 30 nm or more than the peak wavelength of the photoluminescence from the quantum well layer in the region other than the region directly under the film. That is, SiO _x The quantum well layer directly under the film is SiO _x A window region having a wider forbidden band than that of the region directly below the film is formed.
[0059]
Next, the surface of the substrate 1 which is the back surface of the wafer subjected to the thermal annealing is smoothed by buffing. Since the back side of the wafer is directly heated by the lamp without being covered, if there is a morphological deterioration due to loss of As, the resist or organic matter is adsorbed to the rough part of the back side in the subsequent photolithography process, and in the normal cleaning process Removal becomes difficult, and impurities are brought into the subsequent MOCVD epitaxial growth process, leading to poor epitaxial growth and deterioration of crystallinity. By buffing and smoothing the backside of the substrate, the process controllability is improved without introducing impurities into subsequent processes.,Good reproducibility was obtained, and the device yield could be improved.
[0060]
Next, striped SiO _x Without removing the film 10, the p-type GaAs contact layer 11 (carrier concentration 4 × 10 6 is formed by the third MOCVD method.¹⁸cm^-3, Thickness 3-50μm setting) SiO _x It is selectively formed in a region other than where the film 10 is formed. In order to perform selective growth only in the region where the GaAs cap layer 7 is exposed, low pressure MOCVD growth at a temperature of 700 ° C. and a pressure of 76 Torr was performed (FIG. 2F). Further, a p-electrode 12 is formed on the upper surface, and an n-electrode 13 is formed on the lower surface.
[0061]
Next, 40 μm wide SiO _x While confirming the region where the film 10 is formed, a scribe line is inserted in the center of the region, and the length of the resonator is divided into bars to form a resonator. At this time, even if the p-side electrode is formed on the entire surface, SiO 2 _x Since the p-type GaAs contact layer 11 is not formed on the film 10, it can be easily observed from the top surface of the wafer. _x A region where the film 10 is formed can be confirmed. Finally, a reflective film is coated on the light emission on both sides of the bar, and further divided into chips to form individual elements.
[0062]
In this manner, an element having a window region of about 20 μm at both light emitting end faces of a resonator having a length of 800 μm is manufactured. In addition, SiO is directly above the window region. _x Since the film 10 remains formed, current injection into the window region is prevented, and the reactive current is reduced.
[0063]
The semiconductor laser of the present embodiment has a stripe-shaped SiO. _x The film 10 forms a current non-injection region and a disordered window region of the active layer by self-alignment. Therefore, compared with a conventional semiconductor laser element in which both regions are formed in separate steps, precise alignment between both regions is not required, and characteristic defects due to misalignment do not occur. Further, since the p-type GaAs contact layer 11 is selectively formed in a portion other than the window region, it can be easily observed from the top surface of the wafer. _x The window region in which the film 10 is formed can be confirmed, and even when the resonator is formed by cleavage, the resonator can be easily formed so that the cleavage position is not injected with current and includes the window region.
[0064]
SiO _x As the film thickness of the film 10 increases, its volume increases, so the amount of sucking up Ga also increases, resulting in an increase in the generated Ga vacancies and increasing the band gap of the quantum well layer. It is valid. However, if the layer thickness exceeds 1000 nm, GaAs and SiO during the thermal annealing will be described. _x Due to the stress resulting from the difference in thermal expansion coefficient _x The problem of cracks in the film arises. As a result, SiO _x If the film cracks, the thermal stress acting on the wafer is released and the diffusion of Ga vacancies is hindered. Therefore, SiO _x The layer thickness of the film 10 needs to be 100 nm or more and 1000 nm or less, more preferably 300 nm or more and 600 nm or less.
[0065]
Next, semiconductor lasers were manufactured by changing the length of the window region formed in the vicinity of the light emitting end face. In the present embodiment, since the window region and the current non-injection region are formed in a self-aligned manner, the length of the window region matches the length of the current non-injection region. FIG. 5 shows the relationship between the length of the window region, that is, the current non-injection region, the operating voltage of the semiconductor laser element, and the COD level. If the length of the window region is less than 10 μm, the leakage current to the window region is large and a sufficient non-injection effect cannot be obtained, so that the COD level is lowered. On the other hand, when the length of the window region exceeded 60 μm, the COD level was high, but the operating voltage increased because the current path was narrowed. Therefore, in the semiconductor laser device of the present invention, the length of the window region in which the band gap of the quantum well layer formed in the vicinity of the light emitting end face is made larger than the inside of the resonator needs to be 10 μm to 60 μm, more preferably In addition, it is desirable that the thickness is 20 μm to 40 μm in terms of ease of forming a resonator and the number of elements that can be obtained per wafer.
[0066]
Also, by changing the thermal annealing conditions, _x Semiconductor laser devices having different Δλ between the band gap wavelength λw of the quantum well active layer immediately below the film and the band gap wavelength λa of the quantum well active layer inside the resonator were manufactured. First, thermal annealing was performed at a temperature of 850 ° C., a temperature increase rate of 80 ° C./second, and a holding time of 1 minute, thereby manufacturing a semiconductor laser device having Δλ = λa−λw of 9 nm. However, COD degradation occurred at 180 mW due to increased light absorption at the light exit end face.
[0067]
Next, a semiconductor laser device having a Δλ of 55 nm was fabricated by setting the annealing conditions to a temperature of 1000 ° C. or higher, a temperature increase rate of 100 ° C./second, and a holding time of 1 minute. However, COD degradation occurred at 230 mW due to a decrease in crystallinity near the light emitting end face.
[0068]
Therefore, in the semiconductor laser device of the present invention, Δλ needs to be in the range of 10 nm ≦ Δλ = λa−λw ≦ 50 nm, and more preferably 20 nm ≦ to prevent the absorption of the window region and prevent deterioration of crystallinity. It is desirable that Δλ = λa−λw ≦ 40 nm.
[0069]
FIG. 6 shows a life test result of the semiconductor laser device of the first embodiment. From FIG. 6, it was confirmed that the semiconductor laser device of this embodiment continued stable running for over 1000 hours in an aging test at 70 ° C. and CW of 120 mW. In addition, as a result of conducting a COD test of the semiconductor laser device of this embodiment, it was confirmed that COD was free even at an optical output of 300 mW or more.
[Embodiment 2]
FIG. 7 is a cross-sectional view showing the structure of the semiconductor laser device according to the second embodiment of the present invention. 7A is a perspective view including a light emitting end surface, FIG. 7B is a cross-sectional view of a waveguide taken along line Ia-Ia in FIG. 7A, and FIG. 7C is a layer thickness taken along line Ib-Ib in FIG. It is sectional drawing of a direction. In FIG. 7, 701 is an n-type GaAs substrate, and 702 is an n-type Al._0.5Ga_0.5As first cladding layer, 703 is Al_0.3Ga_0.7Non-doped quantum well active layer including As guide layer (8 nm thick Al_0.1Ga_0.92 As well layers and 5nm thick Al between them_0.35Ga_0.65704 is p-type Al._0.5Ga_0.5As second cladding layer, 705 is a p-type etching stop layer, and 706 is a p-type Al made of ridge stripes in the cavity direction._0.5Ga_0.5As third cladding layer, 707 is a p-type GaAs cap layer, and 708 is a p-type Al made of a ridge stripe._0.5Ga_0.5N-type Al formed to fill the side surface of the As third cladding layer_0.7Ga_0.3As current blocking layer, 709 is a p-type GaAs planarization layer, 710 is a SiO formed in a stripe shape in a direction perpendicular to the ridge stripe _x A film, 711 is a p-type GaAs contact layer, 712 is a p-side electrode, and 713 is an n-side electrode. 714 is SiO _x This is a region where the band gap of the quantum well active layer 703 directly under the film is larger than the band gap of the quantum well active layer 703 inside the resonator.
[0070]
Next, a method for manufacturing the semiconductor laser device of this embodiment will be described with reference to FIG.
[0071]
n-type GaAs substrate 701 (carrier concentration 2 × 10¹⁸cm^-3N-type Al by MOCVD_0.5Ga_0.5As first cladding layer 702 (carrier concentration 8 × 10¹⁷cm^-3, Thickness 2 μm), undoped quantum well active layer 703 including guide layer, p-type Al_0.5Ga_0.5As second cladding layer 704 (carrier concentration 1 × 10¹⁸cm^-3, Thickness 0.2 μm), p-type etching stop layer 705, p-type Al_0.5Ga_0.5As third cladding layer 706 (carrier concentration 2 × 10¹⁸cm^-3, Thickness 1.1 μm), p-type GaAs cap layer 707 (carrier concentration 2 × 10¹⁸cm^-3, Thickness 0.7 μm) is epitaxially grown (FIG. 8A). Then, using a known photolithography technique and etching technique, the p-type GaAs layer 707 and the p-type Al_0.5Ga_0.5The As third cladding layer 706 is processed into a stripe-shaped ridge 715 having a width of about 3 μm (FIG. 8B). Further, the p-type GaAs layer 707 and the p-type Al are formed by MOCVD._0.5Ga_0.5The side surface of the ridge formed of the second upper cladding layer 706 on the As is n-type Al._0.7Ga_0.3As block layer 708 (carrier concentration 1 × 10¹⁸cm^-31 μm) and a p-type GaAs planarization layer 709 (FIG. 8C), and then an unnecessary layer formed on the ridge is selectively removed to planarize the surface (FIG. 8D). )).
[0072]
Next, by plasma CVD and photolithography, SiO stripes with a width of 40 μm are formed in a direction perpendicular to the ridge stripe. _x A film (500 nm) 710 is formed (FIG. 8E). The stripe pitch was 800 μm, the same as the resonator length. Next, capless annealing by rapid thermal annealing (RTA) method is performed to form SiO. _x The band gap of the quantum well layer 714 immediately below the film 710 is made larger than the band gap of the quantum well active layer 703 inside the resonator. The annealing conditions were a temperature of 950 ° C., a temperature increase rate of 100 ° C./second, and a holding time of 1 minute. In this annealing, SiO _x From the surface of the p-type GaAs layer 7 and the p-type GaAs planarization layer 709 directly under the film 710, Ga atoms are converted into SiO. _x It is sucked into the film 710 and Ga vacancies are generated inside the GaAs crystal. The Ga vacancies have a large diffusion constant, and diffuse at a stretch toward the GaAs substrate 701, making the band gap of the quantum well active layer 714 larger than the band gap of the quantum well active layer 703 inside the resonator. The manufacturing process so far is the same as that in the first embodiment.
[0073]
Next, striped SiO _x Without removing the film 710, the p-type GaAs contact layer 711 (carrier concentration 4 × 10 6 is formed by MOCVD).¹⁸cm^-3, Thickness 3-50μm setting) SiO _x It is formed flat on the entire surface of the region where the film 710 is formed and the region where the p-type GaAs planarization layer 709 is exposed. That is, the growth temperatureDegree 6By using an atmospheric pressure MOCVD method at 50 ° C. and a pressure of 760 Torr, the GaAs cap layer 707 is also made of SiO. _x A p-type GaAs contact layer 711 is also formed on 710 at substantially the same speed. Further, a p-electrode 712 is formed on the upper surface and an n-electrode 713 is formed on the lower surface (FIG. 8F).
[0074]
Next, 40 μm wide SiO _x A scribe line is put on the marker formed in the approximate center of the region where the film 710 is formed, and is divided into bars in the length of the resonator to form the resonator. At this time, although the p-type GaAs contact layer 711 is formed almost flat on the surface of the wafer, _x Since the polycrystalline p-type GaAs contact layer 711 is formed on the film 710, the morphology is changed only in this region, and since there are some steps, it is observed from the upper surface of the wafer. Easy SiO _x A region where the film 710 is formed can be confirmed. Finally, the light emitting end faces on both sides of the bar are coated with a protective film that also controls the reflectivity, and divided into chips to form individual elements. In this manner, an element having a window region of about 20 μm at both light emitting end faces of a resonator having a length of 800 μm is manufactured. In addition, SiO is directly above the window region. _x Since the film 710 remains formed, current injection into the window region is prevented and reactive current is reduced. Further, since the p-type GaAs contact layer 711 is formed flat on the surface of the chip, it is possible to mount upside down, and the distance between the active layer and the heat sink can be shortened. Temperature characteristics are also improved. Similar to the semiconductor laser device of the first embodiment, the device characteristics were COD free even when the maximum light output was 300 mW or more, and stable running was confirmed over 1000 hours in an aging test at 70 ° C. and CW of 120 mW.
[Embodiment 3]
The manufacturing process of the semiconductor laser device of the third embodiment is performed by using striped SiO in the manufacturing process of the semiconductor laser device of the first and second embodiments. _x The film is formed by sputtering, and the other steps are the same as those in the first and second embodiments. SiO by sputtering _x The film formation conditions were an RF power of 400 W, a substrate temperature of 300 ° C., a gas pressure of 2.5 mTorr, a film thickness of 500 nm, and a mixed gas of argon and oxygen was used. In addition, the wafer is mounted in the chamber of the sputtering apparatus, and SiO 2 _x After the reverse sputtering is performed immediately before forming the wafer and the wafer surface is cleaned, the SiO 2 is subsequently cleaned. _x Formed. Note that an argon single gas was used during reverse sputtering. This is because when a natural oxide film is formed on the p-type GaAs cap layer on the wafer surface in the atmosphere, the SiO of Ga _x In order to inhibit the wicking reaction into the SiO 2 _x Is effectively removed in situ immediately before the formation of, and point defects due to plasma damage are newly generated on the surface of the cap layer to promote the diffusion of Ga vacancies.
[0075]
Furthermore, SiO 2 can be sputtered. _x When forming a film, applying a DC bias of 2 kV or more to the substrate causes more plasma damage to the surface of the cap layer, causing more point defects in the cap layer, and further diffusion of Ga vacancies. Can be promoted. As a result, even if the annealing conditions are low-temperature short-time annealing with a temperature of 850 ° C. and a holding time of 30 seconds, SiO 2 is the same as in the first embodiment.₂The quantum well layer directly under the film is SiO₂A wavelength shift of about 30 nm or more was confirmed from the region other than the region directly under the film, and a window region having a wide forbidden band could be formed effectively. In this embodiment, the sputtering method is used for SiO. _x More preferably, the annealing conditions in the case of forming are set to a temperature rising rate of 100 ° C./second or more, a processing temperature of 800 ° C. to 900 ° C., and a processing time of 30 to 60 seconds. Further, the device characteristics were the same as those of the semiconductor laser device of the first embodiment.
[Embodiment 4]
FIG. 9 is a cross-sectional view of the semiconductor laser device of the fourth embodiment. This is a cross-sectional view of an AlGaInP semiconductor laser having an oscillation wavelength of 635 nm to 680 nm. 9A is a perspective view including a light emitting end surface, FIG. 9B is a cross-sectional view of a waveguide taken along line Ia-Ia in FIG. 9A, and FIG. 9C is a layer thickness taken along line Ib-Ib in FIG. It is sectional drawing of a direction. An n-type GaAs substrate 901 (carrier concentration 2 × 10¹⁸cm^-3) N-type In_0.5 (Al_0.7Ga_0.3)_0.5P lower cladding layer 902 (carrier concentration 8 × 10¹⁷cm^-3, Thickness 1000 nm), non-doped In_0.5(Al_0.5Ga_0.5)_0.5Non-doped InAlGaP multiple quantum well layer 903 including a P light guide layer (In thickness of 7 m)_0.5Ga_0.58 nm thick In sandwiched between 4 P-well layers and the well layers_0.5(Al_0.4Ga_0.6)_0.53 layers of P light barrier layer), p-type In_0.5 (Al_0.7Ga_0.3)_0.5First cladding layer 904 on P (carrier concentration 1 × 10¹⁸cm^-3, Thickness 300 nm), etching stop layer 905, p-type In_0.5 (Al_0.7Ga_0.3)_0.5P second cladding layer 906 (carrier concentration 2 × 10¹⁸cm^-3, Thickness 1000 nm), p-type GaAs layer 907 (carrier concentration 3 × 10¹⁸cm^-3, A thickness of 500 nm). Thereafter, similarly to the semiconductor laser device manufacturing method of the first embodiment, the p-type GaAs layer 907 and the p-type In are used by using a known photolithography technique and etching technique._0.5 (Al_0.7Ga_0.3)_0.5The second upper cladding layer 906 on P is processed into a striped ridge 916 having a width of 4 to 5 μm. Next, by the second MOCVD method, the p-type GaAs layer 907 and the p-type In_0.5 (Al_0.7Ga_0.3)_0.5The side surface of the ridge 916 made of the second cladding layer 906 on the P is n-type GaAs current blocking layer 908 (carrier concentration 1 × 10 6¹⁸cm^-3, Thickness 1000 nm) and p-type GaAs planarization layer 909 (carrier concentration 2 × 10¹⁸cm^-3Then, the unnecessary layer formed on the ridge 916 is selectively removed to flatten the surface. Next, by a plasma CVD method and a photolithography method, a 40 μm wide SiO 2 stripe is formed in a direction perpendicular to the ridge stripe 916. _x A film (thickness 500 nm) 910 is formed. The stripe pitch was 800 μm, the same as the resonator length. Next, capless annealing by rapid thermal annealing (RTA) method is performed to form SiO. _x The band gap of the quantum well layer 914 immediately below the film 910 is made larger than the band gap of the quantum well active layer 903 inside the resonator. The annealing conditions were a temperature of 850 ° C., a temperature increase rate of 100 ° C./second, and a holding time of 1 minute, and the same method as in the first embodiment was performed. As in the case of the AlGaAs semiconductor laser device of the first embodiment, in this annealing, SiO 2 _x From the surface of the p-type GaAs layer 907 and the p-type GaAs planarization layer 909 directly under the film 810, Ga atoms are converted into SiO. _x It is sucked into the film 910 and Ga vacancies are generated inside the GaAs crystal. The Ga vacancies are diffused all at once toward the GaAs substrate 901, and the band gap of the quantum well active layer 914 is increased. Next, striped SiO _x Without removing the film 910, the p-type GaAs contact layer 911 (4 × 10 4 is formed by the third MOCVD method.¹⁸cm^-3, A thickness of 3 to 10 μm) is formed almost flat on the entire surface. SiO on GaAs _x In order to form the p-type GaAs contact layer 911 at a substantially same speed, the growth is performed by atmospheric pressure MOCVD at a growth temperature of 650 ° C. and a pressure of 760 Torr. Further, a p-electrode 912 is formed on the upper surface, and an n-electrode 913 is formed on the lower surface.
[0076]
Next, 40 μm wide SiO _x A scribe line is put on the marker formed in the approximate center of the region where the film 910 is formed, and the resonator is divided into bars to form the resonator. At this time, although the p-type GaAs contact layer 911 is formed flat on the surface of the chip, _x Since the p-type GaAs contact layer 915 formed on the film 910 is polycrystalline, the morphology changes only in this region, and it is easy to observe even from the top surface of the wafer. _x A window region in which the film 910 is formed can be confirmed. Finally, a reflective film is coated on the light emission on both sides of the bar, and further divided into chips to form individual elements. In this manner, an element having a window region of about 20 μm at both light emitting end faces of a resonator having a length of 800 μm is manufactured. In addition, SiO is directly above the window region. _x Since the film 910 remains formed, current injection into the window region is prevented and reactive current is reduced. The obtained device characteristics were COD-free even when the maximum light output was 100 mW or more, and stable running was confirmed over 3000 hours in an aging test at 70 ° C. and CW 40 mW.
[0077]
In the semiconductor laser devices of the first to fourth embodiments described above, all crystal growth is described by the MOCVD method, but a vapor phase growth method such as MBE method, ALE, or VPE method, which has a quantum well structure. Needless to say, any material that can be manufactured is applicable.
[0078]
【The invention's effect】
As described above, according to the semiconductor laser device of the present invention, the semiconductor laser device of the present invention includes the first conductivity type first cladding layer, the quantum well active layer, the first conductivity type substrate, A second conductivity type second cladding layer, a second conductivity type third cladding layer comprising ridge stripes in the direction of the resonator, and a first conductivity type current configured to embed ridge stripe side surfaces of the third cladding layer A block layer and a cap layer of the second conductivity type formed on the third cladding layer, a dielectric film formed in a direction perpendicular to the ridge stripe in the vicinity of the resonator end face on the cap layer, and the dielectric layer Since the band gap of the quantum well active layer directly below the body film is larger than the band gap of the quantum well active layer inside the resonator, the dielectric film near the resonator end face has a large band gap of the quantum well active layer. To prevent current injection into the window regions have, a reactive current is reduced, a semiconductor laser device excellent in high output characteristics and reliability can be obtained. Furthermore, since the end face window formation and the current non-injection region formation can be formed by self-alignment, it is excellent in mass productivity and can realize cost reduction by improving yield.
[0079]
In addition, by selectively providing a second conductivity type contact layer on the cap layer other than the dielectric film, a window region having a large band gap of the quantum well active layer in the vicinity of the cavity end face can be easily confirmed after the process is completed. In addition, the cleaving process for forming the resonator is facilitated, so that mass production is excellent and the yield is improved.
[0080]
Further, a second conductivity type contact layer is formed in both the region of the cap layer where the dielectric film is formed and the region where the dielectric film is not formed, and the dielectric film of the contact layer is formed. A window region can be identified by providing a step or a difference in morphology between a portion formed on the region where the dielectric film is not formed and a portion formed on the region where the dielectric film is not formed. Since the second conductivity type contact layer exists almost flatly on the upper surface of the cap layer on which the dielectric film is not formed, the semiconductor laser element can be mounted upside down, and heat dissipation can be promoted. Temperature characteristics can be improved.
[0081]
Further, the difference Δλ between the band gap wavelength λw of the quantum well active layer immediately below the dielectric film and the band gap wavelength λa of the quantum well active layer inside the resonator is set in a range of 10 nm ≦ Δλ = λa−λw ≦ 50 nm. As a result, the COD level decreases due to the increase in light absorption at the light emitting end face when Δλ = λa−λw is less than 10 nm, and the crystal defects increase near the end face when Δλ = λa−λw is 50 nm or more and the non-light emission associated therewith. A function as a window structure can be secured by preventing a decrease in the COD level due to an increase in the center.
[0082]
Further, the cap layer of the second conductivity type is made of Al._xGa_1-xAs (x ≦ 0.1)WhenAl containing a large amount of Al on the surface on which the dielectric film is formed_xGa_1-xEven in the case of As (x> 0.1), it is possible to prevent the formation of Ga vacancies by inhibiting the absorption of Ga by Al and to promote the reaction that effectively increases the band gap of the quantum well active layer. .
[0083]
Further, by setting the film thickness of the second conductivity type cap layer in the range of 100 nm to 1000 nm, the Al dielectric film from the third cladding layer when the film thickness of the second conductivity type cap layer is less than 100 nm. The generation of Ga vacancies due to the inhibition of Ga absorption due to diffusion, and the band gap of the quantum well layer is increased by increasing the distance from the dielectric film to the quantum well layer when the thickness of the cap layer is 1000 nm or more. The reaction for increasing the band gap of the quantum well active layer can be promoted by preventing the deterioration of device characteristics due to the diffusion of the dopant present in the crystal due to the fact that the thermal annealing conditions for performing the annealing must be performed at a higher temperature for a longer time.
[0084]
The dielectric film formed in the vicinity of the resonator end face is made of SiO. _x By so doing, it is possible to promote a reaction that effectively increases the band gap of the quantum well active layer.
[0085]
In addition, by setting the thickness of the dielectric film in the range of 100 nm to 1000 nm, it is possible to increase the band gap of the quantum well active layer to the extent that the function as the window structure can be sufficiently exhibited.
[0086]
Further, by setting the length of the region where the band gap of the quantum well active layer in the vicinity of the resonator end face is larger than the band gap of the quantum well active layer inside the resonator to 10 μm or more and 60 μm or less, leakage current to the end face is reduced. It is possible to suppress the degradation of the efficiency of the device due to free carrier loss.
[0087]
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor laser device comprising: a first conductivity type first cladding layer; a quantum well active layer; a second conductivity type second cladding layer; An etching stop layer, a second conductivity type third cladding layer, and a second conductivity type cap layer are sequentially epitaxially grown, and the second conductivity type third cladding layer and the second conductivity type cap layer are formed in the resonator direction. Forming a ridge stripe into the ridge stripe, embedding the side surface of the ridge stripe with a current block layer of the first conductivity type, and removing a current block unnecessary layer simultaneously formed on the ridge when the current block layer is embedded to flatten the surface. The step of forming the dielectric film in the direction perpendicular to the ridge stripe, and the amount of the band gap of the quantum well active layer directly under the dielectric film by thermal annealing in the amount inside the resonator. A step of increasing the band gap of the well active layer, a step of forming a contact layer of the second conductivity type while leaving the dielectric film, and a quantum well active layer having a light emission end face larger than the inside of the resonator. Forming a resonator so as to be in the region, the stripe-shaped dielectric film used to increase the band gap of the quantum well active layer in the vicinity of the cavity end face is directly applied to the band of the quantum well active layer. It has the role of preventing current injection into the window region with a large gap, and the end face window formation and the current non-injection region formation can be formed by self-alignment, which eliminates the need to align the window region and the non-injection region, simplifying the process. Can be measured.
[0088]
Further, in the step of forming the dielectric film, after forming a resist pattern having an opening and forming the dielectric film on the entire surface, the dielectric film formed on the resist is lifted off to form the dielectric film. If formed, the regions other than the window do not cause plasma damage when the dielectric film is formed because there is a resist. Therefore, the controllability for suppressing the band cap expansion of the quantum well active layer in the region other than the window and selectively increasing the band gap only in the window region is improved. In addition, a window structure forming process can be provided without deteriorating the crystallinity of regions other than the window.
[0089]
In addition, the dielectric film is formed by either sputtering or plasma CVD, and at the same time as the formation of the dielectric film, a new point defect due to plasma damage is generated on the surface, which can further promote the diffusion of Ga vacancies. Therefore, an effective window region can be formed.
[0090]
The conditions for forming the dielectric film for increasing the band gap of the quantum well active layer immediately below the dielectric film by plasma CVD are as follows: RF power is 100 W or more, substrate temperature is 250 ° C. When the temperature is set to 350 ° C. and the thickness of the dielectric film is set to 100 nm or more and less than 1000 nm, point defects due to plasma damage can be more effectively generated on the surface, and diffusion of Ga vacancies can be further promoted. Adhesiveness between the cap layer and the dielectric film can be maintained by adjusting the temperature to from 350C to 350C. By setting the thickness of the dielectric film to 100 nm or more and less than 1000 nm, it is possible to increase the band gap of the quantum well active layer to the extent that the function as the window structure can be sufficiently exhibited.
[0091]
The conditions for forming the dielectric film for enlarging the band gap of the quantum well active layer immediately below the dielectric film by sputtering are as follows: RF power is 200 W or more, and substrate temperature is 250 ° C. to 350 ° C. When the dielectric formation film thickness is 100 nm or more and less than 1000 nm, it is possible to more effectively generate point defects due to plasma damage on the surface, promote the diffusion of Ga vacancies, and the substrate temperature is 250 ° C. to 350 ° C. By doing so, the adhesion between the cap layer and the dielectric film can be maintained. Furthermore, by setting the thickness of the dielectric film to 100 nm or more and less than 1000 nm, it is possible to increase the band gap of the quantum well active layer to such an extent that the function as the window structure can be sufficiently exhibited.
[0092]
Also, reverse sputtering is performed on the cap layer of the second conductivity type just before forming a dielectric film for enlarging the band gap of the quantum well active layer immediately below the dielectric film by sputtering to clean the substrate surface. By providing the step of performing crystallization, the SiO of Ga _x The natural oxide film formed on the cap layer that hinders the wicking reaction into the cap layer can be effectively removed in situ, and a point defect due to plasma damage is newly generated on the surface of the cap layer. Can promote diffusion.
[0093]
In the step of forming a dielectric film for increasing the band gap of the quantum well active layer immediately below the dielectric film on the second conductivity type cap layer by sputtering, a DC bias of 2 kV or more is applied to the substrate. By providing the step of applying, SiO _x At the same time as the formation of, more point defects due to plasma damage are generated on the surface of the cap layer, and diffusion of Ga vacancies can be promoted.
[0094]
Further, as thermal annealing conditions for making the band gap of the quantum well active layer immediately below the dielectric film larger than the band gap of the quantum well active layer inside the resonator, the temperature rising rate is 80 ° C./second or more, the processing temperature is 800 ° C. By realizing a process time of 10 to 60 seconds at ~ 1000 ° C, it is possible to achieve both the promotion of Ga vacancy diffusion and the suppression of dopant diffusion inside the crystal, and the formation of window regions without deteriorating device characteristics. It can be done.
[0095]
Preferably, as a thermal annealing method for making the band gap of the quantum well active layer immediately below the dielectric film larger than the band gap of the quantum well active layer inside the resonator, a lamp heating from one side of the back side of the substrate is used. In addition, by performing the epitaxial growth surface in contact with another substrate, it is possible to prevent surface roughness and crystallinity degradation due to As missing from the cap layer on the epitaxial growth surface.
[0096]
In addition, by buffing and smoothing the back surface of the substrate after the thermal annealing step, As is lost on the back surface side of the substrate by direct lamp heating, and the morphology of the back surface of the substrate is roughened. And organic substances are adsorbed on the rough part of the back surface, making it difficult to remove them by a normal cleaning process, and subsequently introducing impurities during the epitaxial process, leading to poor epitaxial growth and poor crystallinity. Good controllability,Good reproducibility can be obtained and the device yield can be improved.
[Brief description of the drawings]
FIG. 1 is a perspective view showing the structure of a semiconductor laser device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a manufacturing process of the semiconductor laser device according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view of an annealing apparatus used for an annealing step in the method of manufacturing a semiconductor laser device according to the first embodiment of the present invention.
4 is a diagram showing microphotoluminescence (a) in the vicinity of the end face of the quantum well layer of the semiconductor laser device according to the first embodiment of the present invention and microphotoluminescence (b) in a region other than the vicinity of the end face. FIG.
FIG. 5 is a diagram showing the relationship between the current non-injection width, the COD level, and the operating voltage of the semiconductor laser device according to the first embodiment of the present invention.
FIG. 6 is a diagram showing an aging test result of the semiconductor laser device according to the first embodiment of the present invention.
FIG. 7 is a perspective view showing the structure of a semiconductor laser device according to a second embodiment of the present invention.
FIG. 8 is a diagram illustrating a manufacturing process of a semiconductor laser device according to a second embodiment of the present invention.
FIG. 9 is a perspective view showing the structure of a semiconductor laser device according to a fourth embodiment of the present invention.
FIG. 10 is a perspective view showing the structure of a conventional semiconductor laser device.
FIG. 11 is a diagram illustrating a manufacturing process of a conventional semiconductor laser device.
[Explanation of symbols]
1,701 n-type GaAs substrate
2,702 n-type Al_0.5Ga_0.5As first cladding layer
3,703 Undoped quantum well active layer including guide layer
4,704 p-type Al_0.5Ga_0.5As second cladding layer
5,705 p-type etching stop layer
6,706 p-type Al_0.5Ga_0.5As third cladding layer
7,707,807 p-type GaAs cap layer
8,708 n-type AlGaAs block layer
9, 709, 809 n-type AlGaAs block layer
10, 710 SiO _x film
11,711,811 p-type GaAs contact layer
12,712 p-side electrode
13, 713, 813 n-side electrode
14, 714 Region where the band gap of the quantum well active layer is larger than the band gap of the quantum well active layer inside the resonator
715 SiO _x Polycrystalline p-type GaAs contact layer formed on the film
101 Striped resist mask
102,716 p-type GaAs layers 7,707 and p-type Al_0.5Ga_0.5Striped ridge comprising As third cladding layers 6 and 706
901 n-type GaAs substrate
902 n-type In_0.5(Al_0.7Ga_0.3)_0.5P first cladding layer
903 Undoped In_0.5(Al_0.7Ga_0.3)_0.5Undoped InAlGaP multiple quantum well layers (In_0.5Ga_0.5P well layer 7nm and In_0.5(Al_0.7Ga_0.3)_0.5(P light barrier layer is composed of 8nm 4 cycles)
904 p-type In_0.5(Al_0.7Ga_0.3)_0.5P second cladding layer
905 p-type etching stop layer
906 p-type In_0.5(Al_0.7Ga_0.3)_0.5P third cladding layer
907 p-type GaAs cap layer
908 n-type GaAs block layer
909 p-type GaAs planarization layer
910 SiO _x film
911 p-type GaAs contact layer
912 p-side electrode
913 n-side electrode
914 Region where the band gap of the quantum well active layer is larger than the band gap of the quantum well active layer inside the resonator
915 SiO _x Polycrystalline p-type GaAs contact layer formed on the film
916 p-type GaAs layer 7 and p-type In_0.5(Al_0.7Ga_0.3)_0.5Striped ridge made of P third cladding layer 6
1001 GaAs substrate
1002 n-type AlGaAs lower cladding layer
1003 Quantum well active layer
1003a region contributing to laser oscillation of the quantum well active layer 1003,
1003b Window structure region formed near laser cavity end face 1020 of quantum well active layer 1003
1004a p-type AlGaAs first upper cladding layer
1004b p-type AlGaAs second upper cladding layer,
1005 p-type GaAs contact layer
1006 Hole diffusion region (shaded area)
1007 Proton injection region
1008 n-side electrode
1009 p-side electrode
1010a SiO₂Striped opening of film 1011
1011 SiO₂Resist formed in the same region as the stripe-shaped opening 1010a of the film 1010
1020 End face of laser resonator

Claims (18)

On the first conductivity type substrate, the first conductivity type first cladding layer, the quantum well active layer, the second conductivity type second cladding layer, and the second conductivity type second cladding layer formed of ridge stripes in the resonator direction. A semiconductor comprising: 3 cladding layers; a first conductivity type current blocking layer configured to embed a ridge stripe side surface of the third cladding layer; and a second conductivity type cap layer formed on the third cladding layer In the laser element,
A dielectric film is formed in the direction perpendicular to the ridge stripe in the vicinity of the resonator end face on the cap layer,
The band gap of just below the dielectric film of the quantum well active layer is much larger than the band gap of the resonator,
Semiconductor laser over laser device, characterized in that the dielectric region not formed with the film on the cap layer is provided a contact layer of the second conductivity type. The semiconductor laser device according to claim 1,
A contact layer of a second conductivity type is formed in both the region of the cap layer where the dielectric film is formed and the region where the dielectric film is not formed;
A semiconductor provided with a step difference or a morphological difference between a portion of the contact layer formed on the region where the dielectric film is formed and a portion formed on the region where the dielectric film is not formed Laser element. The semiconductor laser device according to claim 1,
A semiconductor laser in which the difference Δλ between the band gap wavelength λw of the quantum well active layer immediately below the dielectric film and the band gap wavelength λa of the quantum well active layer inside the resonator is in the range of 10 nm ≦ Δλ = λa−λw ≦ 50 nm element. The semiconductor laser device according to claim 1,
The second conductivity type cap layer is _{Al x Ga 1-x As (} x ≦ 0.1) der Ru semiconductor laser element. The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the second conductivity type cap layer has a thickness of 100 nm to 1000 nm . The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein a dielectric film formed in the vicinity of the end face of the resonator is SiO _x (x is a positive real number) . The semiconductor laser device according to claim 1,
A semiconductor laser device having a thickness of the dielectric film in a range of 100 nm to 1000 nm . The semiconductor laser device according to claim 1,
The band gap of the quantum well active layer in the region near the resonator end face is larger than the band gap of the quantum well active layer in the other region, and the length in the resonator direction of the region with the large band gap is 10 μm or more and 60 μm or less. Semiconductor laser element. A first conductivity type first cladding layer, a quantum well active layer, a second conductivity type second cladding layer, a second conductivity type etching stop layer, and a second conductivity type third cladding on a first conductivity type substrate. Sequentially epitaxially growing a layer and a second conductivity type cap layer;
Processing the second conductivity type third cladding layer and the second conductivity type cap layer into a stripe-shaped ridge in the resonator direction;
Embedding the stripe-shaped ridge side surface with a first conductivity type current blocking layer;
Removing an unnecessary layer formed simultaneously on the ridge in the step of embedding the current blocking layer, and planarizing the surface;
Forming a dielectric film in a direction perpendicular to the ridge;
Making the band gap of the quantum well active layer in the region immediately below the dielectric film larger than the band gap of the quantum well active layer in other regions by thermal annealing;
Forming a second conductivity type contact layer while leaving the dielectric film;
Forming a resonator so that a light emitting end face is disposed in a region having a large band gap of the quantum well active layer; and
A method for manufacturing a semiconductor laser device , comprising: In the manufacturing method of the semiconductor laser device according to claim 9,
The step of forming the dielectric film includes a step of processing a resist into a pattern having an opening, forming a dielectric film on the entire surface, and then removing the dielectric film formed on the resist by lift-off . Production method. In the manufacturing method of the semiconductor laser device according to claim 9 ,
The method of manufacturing a semiconductor laser device, wherein the dielectric film is formed by either a sputtering method or a plasma CVD method. In the manufacturing method of the semiconductor laser device according to claim 9 ,
The formation of the dielectric film uses a flop plasma CVD method, an RF power 100W or more, a substrate temperature of 250 ° C. to 350 ° C., the thickness of 100nm or more, the method for manufacturing the semiconductor laser device to be less than 1000 nm. In the manufacturing method of the semiconductor laser device according to claim 9 ,
The formation of the dielectric film using a sputtering method, RF power of 2 00W or more, and the substrate temperature was 250 ° C. to 350 ° C., the film thickness is 100nm or more, the method of manufacturing a semiconductor laser device Ru 1000nm less than der. In the manufacturing method of the semiconductor laser device according to claim 13 ,
The method of manufacturing a semiconductor laser element for cleaning of the surfaces forming a dielectric film by reverse sputtering immediately before forming the dielectric film. In the manufacturing method of the semiconductor laser device according to claim 13 ,
A method of manufacturing a semiconductor laser device, wherein a DC bias of 2 kV or more is applied to a substrate in the step of forming the dielectric film. In the manufacturing method of the semiconductor laser device according to claim 9 ,
The thermal annealing is elevated to the annealing temperature at a heating rate of 80 ° C. / sec or more raised, the annealing temperature is 800 ° C. to 1000 ° C., annealing time 10 seconds to 60 Byodea Ru method of manufacturing a semiconductor laser device. In the manufacturing method of the semiconductor laser device according to claim 9 ,
The method of manufacturing a semiconductor laser device, wherein the thermal annealing is performed by performing lamp heating only from the first conductivity type substrate side and bringing another substrate into contact with the surface on which the dielectric film is formed . In the manufacturing method of the semiconductor laser device according to claim 9 ,
A method of manufacturing a semiconductor laser device , wherein the surface of the first conductivity type substrate is smoothed by buffing after the thermal annealing step .

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