JP2008021908A - Semiconductor laser device and integrated semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device which solves a problem that, since a deep level occurs to narrow a forbidden width due to an adsorption or oxidation of oxygen at an interface between an emission end and a dielectric film, an end temperature rises by a non-light-emitting recombination to increase a light absorption, and a COD (Catastrophic Optical Damage) such as a melting of the end or a breakage of the end occurs; and which is capable of obtaining a high output characteristic and a high reliability. <P>SOLUTION: In the semiconductor laser device, a dielectric reflective film of a mono-layer structure or multi-layer structure is formed on the emission end of laser beams, and a heavy metal impurity concentration of Fe or Cr at an interior of a first dielectric film coming into contact with the emission end and an interface between the first dielectric film and the emission end is set to 3×10<SP>17</SP>atoms/cm<SP>3</SP>or less, to materialize a high reliability suitable for a high output operation. In particular, the semiconductor laser device operates advantageously in an integration semiconductor laser device in which a red semiconductor laser element and an infrared semiconductor laser element are mounted on the same substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device having a single wavelength or a plurality of wavelengths used for a light source of an optical disk.

  Semiconductor lasers are widely used in many fields of electronics and optoelectronics, and are indispensable as optical devices. In particular, optical disc apparatuses such as CD (compact disc) and DVD (digital versatile disc) are currently actively used as large-capacity recording media. A recording medium (media) used for a DVD has a smaller pit length and track interval than a CD medium. Therefore, the wavelength of the semiconductor laser used is shorter for DVD than for CD. Specifically, the oscillation wavelength of the CD laser is in the 780 nm band, whereas the oscillation wavelength of the DVD laser is in the 650 nm band.

  In order for one optical disk device to detect both CD and DVD information, two light sources, a 780 nm band laser (infrared semiconductor laser element) and a 650 nm band laser (red semiconductor laser element) are required. 2. Description of the Related Art In recent years, in order to reduce the size and weight of an optical pickup device that constitutes an optical disk device, a two-wavelength type semiconductor laser element that emits laser light of two types of wavelengths in one semiconductor chip has been developed and spread. It's getting on.

  When writing data on an optical disk, the heat generated by laser light irradiation is used, so that the optical output power is several to several tens of times higher than when data is read from the optical disk. In addition, an increase in recording speed is demanded as the capacity of optical disks increases. Therefore, high output and high reliability are required for the semiconductor laser used in the recording / reproducing optical disc apparatus.

6A and 6B are perspective views of a conventional two-wavelength semiconductor laser device (see, for example, Patent Document 1). This semiconductor laser device includes two laser elements, a red semiconductor laser element a ₀ that emits laser light L1 having a wavelength of 650 nm band and an infrared semiconductor laser element b ₀ that emits laser light L2 having a wavelength of 780 nm band. It is composed of W1 and W2 are laser beam emission windows.

The semiconductor laser device is provided with a separation groove 71 for electrically separating the red semiconductor laser element a ₀ and the infrared semiconductor laser element b ₀ . A p-side electrode 72 is divided and formed on the upper surface of the semiconductor laser device by a separation groove 71, and an n-side electrode 73 is formed on the entire bottom surface thereof. Two p-side electrodes 72 and one n-side electrode are formed. Each of the semiconductor laser elements a ₀ and b ₀ can be operated independently by applying a bias voltage to 73 independently.

  The semiconductor laser device has an emission end face 74 for extracting the laser beams L1 and L2 to the outside, and a rear end face 75 for reflecting and confining the light inside the resonator. A multilayer coat film 76 is laminated on the rear end face 75. On the other hand, end face coat films 77 and 78 having a lower reflectance than the rear end face 75 are formed on the emission end face 74 in order to increase the laser beam extraction efficiency.

In the laser structure disclosed in Patent Document 1, the reflectance of the emission end face is controlled to 24% to 32%, and the reflectance of the red semiconductor laser element for DVD reproduction (DVD-ROM) is reproduced by CD (CD-). A two-wavelength type semiconductor laser set lower than the reflectance of an infrared semiconductor laser element for ROM) has been proposed. Specifically, the film thickness is determined so that the output end face reflectivity of the red semiconductor laser element is 24% and the output end face reflectivity of the infrared semiconductor laser element is 32%. One deposition process (using vapor deposition) Thus, aluminum oxide (Al ₂ O ₃ ) is formed on the emission end face. The aforementioned film thickness is set to λ ₃ / (2n ₃ ) when the wavelength of the infrared semiconductor laser element is λ ₃ and the refractive index of Al ₂ O ₃ is n ₃ (about 1.66). . By this method, a device having substantially the same kink level and COD level between the red semiconductor laser element and the infrared semiconductor laser element is being obtained. The kink level is a light output level at which a kink (bending) occurs in the injection current-light output characteristic. The COD level is a light output level at which COD (Catastrophic Optical Damage), that is, instantaneous optical damage occurs at the emission end face. A higher kink level or COD level is preferable because the resistance is higher.

Further, in Patent Document 2, the reflectance of the emission end face of the red semiconductor laser element used for DVD reproduction (DVD-ROM) is about 20%, and the reflection of the emission end face of the infrared semiconductor laser element used for CD reproduction (CD-ROM). A technique for forming an end face coat film with a rate of about 5% or less has been proposed. This end face coating film is composed of two kinds of materials (for example, Al ₂ O ₃ and SiO ₂ ), and the thickness of each is determined in order to obtain a desired reflectance.

On the other hand, as one effective means for increasing the output, there is known a method in which the reflectance of two end faces forming a resonator of a semiconductor laser is asymmetric. This is a common method for semiconductor lasers used for writing on optical disks. In this method, the end facet forming the resonator is coated with a dielectric multilayer film to make the end face reflectivity asymmetric. Out of the end faces forming the resonator, the output end face has a low reflectivity (about 10%). The reflectance of the rear end face on the opposite side is set to a high reflectance (about 90%). The reflectance of the dielectric multilayer film is controlled by the refractive index, the layer thickness, and the number of layers to be laminated.
JP 2001-320131 A (page 3-4, FIG. 1-2) JP 2002-223030 (page 3-5, Fig. 1-4)

  The multi-wavelength semiconductor laser devices (arrays) disclosed in Patent Document 1 and Patent Document 2 provide a suitable end surface coat forming technique within a limited range of reproduction-only, such as DVD-ROM and CD-ROM. Is. These techniques are effective when the semiconductor laser is operated at a low output (for example, a rated output of about 5 mW). However, it is difficult to obtain a high output when writing to an optical recording medium such as a DVD-RAM, DVD-R, or CD-R.

  On the other hand, the conventional technique in which the reflectances of the two end faces are asymmetrical is merely a general technique for obtaining a high output operation, and a multi-wavelength in which semiconductor lasers having a plurality of oscillation wavelengths are formed on the same substrate. It is difficult to say that conditions suitable for a semiconductor laser are presented, and it is difficult to guarantee a sufficient lifetime during high-power operation.

  When further increasing the output of a semiconductor laser, the generation of COD (instantaneous optical damage) on the cavity end face becomes a major problem. In particular, in an AlGaInP semiconductor laser suitable for a red semiconductor laser in the 650 nm band, COD (instant optical damage) on the cavity end face is pointed out as an important cause of deterioration that determines the life of the laser during high-power operation. Has been.

  COD (instantaneous optical damage) occurs because the vicinity of the cavity end face of the semiconductor laser is an absorption region for light generated inside the laser. This is because a deep level is generated on the semiconductor surface due to oxygen adsorption and surface oxidation on the semiconductor surface of the cavity end face, and the forbidden band width of the semiconductor is substantially narrowed. The end face temperature rises due to non-radiative recombination via deep levels existing on the semiconductor surface, and this temperature rise causes a cycle in which the forbidden band width near the end face is further reduced and light absorption is increased. When this cycle becomes positive feedback, melting of the end face or destruction of the end face occurs. This is COD (instantaneous optical damage).

  In the contents described above, the generation of deep levels due to oxidation is a problem, but the improvement of high output in the AlGaInP semiconductor laser has not been realized.

  The present invention has been created in view of such circumstances, and an object thereof is to provide a semiconductor laser device capable of obtaining high output characteristics and high reliability.

In the semiconductor laser device according to the present invention, a dielectric reflection film having a single-layer structure or a multi-layer structure is formed on an emission end face of a laser beam, and the inside of the first dielectric film in contact with the emission end face and the first dielectric film and the The heavy metal impurity concentration at the interface with the emission end face is set to 3 × 10 ¹⁷ atoms / cm ³ or less.

In this configuration, the dielectric reflection film is a single layer or a multilayer, but in any case, the dielectric film in contact with the emission end face is referred to as a first dielectric film. By setting the concentration of heavy metal impurities contained in the interface between the first dielectric film and the emission end face and in the first dielectric film to 3 × 10 ¹⁷ atoms / cm ³ or less, the semiconductor laser The tolerance at the time of high output operation can be made high.

In the prior art, the generation of deep levels due to oxidation is a problem, but the reliability decreases due to contamination by heavy metal impurities such as Fe, Cr and Ni that occur when forming a dielectric reflection film. The perception of is not shown. As a result, it has been difficult to realize a high-power laser especially for an AlGaInP semiconductor laser. The present inventor has found that there is a clear correlation between the concentration of heavy metal impurities and the lifetime, particularly in research during high power operation of red semiconductor laser devices. As a result, in order to realize a lifetime of 1000 hours or more, it is not sufficient to prevent oxidation of the emission end face of the semiconductor laser, and the inside of the first dielectric film in contact with the emission end face and the first dielectric film and the emission end face. It has been found that the concentration of heavy metal impurities at the interface with the substrate should be 3 × 10 ¹⁷ atoms / cm ³ or less. By configuring the semiconductor laser device under such conditions, deep levels generated due to heavy metal impurities at the interface between the emission end face and the first dielectric film can be reduced, resulting in higher output and longer life. It has become possible to achieve both compatibility.
In the case of a red semiconductor laser having an active layer of an AlGaInP-based semiconductor, high reliability can be ensured even in a high output operation of 140 mW or more, and the yield of the integrated semiconductor laser device can be improved.

  In the above configuration, the heavy metal impurity element includes at least one element selected from the group consisting of Fe, Cr, and Ni.

In the above configuration, the dielectric reflection film is composed of the first dielectric film in contact with the emission end face and the second dielectric film formed outside the first dielectric film, and The refractive index n ₁ of the first dielectric film is 1.6 ≦ n ₁ ≦ 2.3, and the refractive index n ₂ of the second dielectric film is 1.4 ≦ n ₂ <1.6. .

In the above structure, the first dielectric film is at least one compound selected from the group consisting of Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , and ZrO ₂ , and the second dielectric film Is preferably SiO ₂ .

Since the dielectric materials Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , and ZrO ₂ have higher barrier properties against heavy metal impurity elements than SiO ₂ , Fe, Cr, Ni contained in the dielectric film The concentration of heavy metal impurities such as is low.

  Then, the dielectric reflection film is composed of a combination of the first and second dielectric films having different refractive indices, and the refractive index of each dielectric reflection film is adjusted as described above, so that the desired reflection at the emission end face. Rate can be obtained. For example, it is possible to set the reflectance at the exit end face in a range of 1 to 7%.

It is also possible to set the light density at the emission end face to 23.6 MW / cm ² or more. Specifically, in a semiconductor laser device operating at 240 mW with a heavy metal impurity concentration of 3 × 10 ¹⁷ atoms / cm ³ or less, a reflectance of the exit end face of 6%, and a reflectivity of the rear end face of 96%, the lifetime is 1000 hours or more. The result of estimating the light density at the exit end face in a simulation that secures the reliability of 23.6 MW / cm ² .

  Of course, the semiconductor laser device having the above-described structure may be applied to a semiconductor laser device having a single oscillation wavelength, but rather, a plurality of semiconductor laser devices having different oscillation wavelengths are disposed on the same substrate. Application to the formed integrated semiconductor laser device is most effective. As a typical integrated semiconductor laser device, the first semiconductor laser device with a shorter oscillation wavelength is an AlGaInP semiconductor material whose active layer material is the semiconductor laser, and the second semiconductor laser device with a longer oscillation wavelength. Has an aspect that the active layer material is an AlGaAs-based semiconductor material. A red semiconductor laser of 650 nm band uses an active layer material as an AlGaInP semiconductor material, and an infrared semiconductor laser of 780 nm band uses an AlGaAs semiconductor material as an active layer material.

  With this configuration, in the integrated semiconductor laser device in which the red semiconductor laser element and the infrared semiconductor laser element are mounted on the same substrate, the heavy metal impurity is formed at the interface between the emission end face and the first dielectric film, as described above. It is possible to reduce the deep level generated due to the above, and to achieve both high output and long life.

According to the present invention, since the heavy metal impurity concentration (for example, Fe, Cr, or Ni) in the first dielectric film formed on the resonator end face is 3 × 10 ¹⁷ atoms / cm ³ or less, the emission end face and the first dielectric Deep levels generated due to heavy metal impurities at the interface with the body film can be reduced, and both high output and long life can be achieved, and the yield of the semiconductor laser can be improved. This is particularly advantageous in an integrated semiconductor laser device in which a red semiconductor laser element and an infrared semiconductor laser element are mounted on the same substrate.

  Embodiments of a semiconductor laser device according to the present invention will be described below in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a perspective view of an integrated semiconductor laser device of the present invention. The present embodiment is an example of a two-wavelength type semiconductor laser device in which a red semiconductor laser element a having an oscillation wavelength in the 650 nm band and an infrared semiconductor laser element b having an oscillation wavelength in the 780 nm band are formed on the same substrate. is there.

  As shown in FIG. 1, the two-wavelength semiconductor laser device according to the present embodiment includes a red semiconductor laser element a that oscillates laser light in the 650 nm band and an infrared semiconductor laser element b that oscillates laser light in the 780 nm band. Are formed monolithically on one substrate 1.

  The red semiconductor laser device a includes an n-type cladding layer 2, an active layer 3, a first p-type cladding layer 4, an etching stop layer 5, and a second p-type cladding layer on an n-type GaAs substrate 1 for epitaxial growth. 6. A p-type contact layer 7 and an insulating layer 8 are sequentially formed.

  The infrared semiconductor laser element b has the same structure as that of the red semiconductor laser element a, although the semiconductor composition is different. The infrared semiconductor laser element b has an n-type cladding layer 12, an active layer 13, and a first layer on the substrate 1. The p-type cladding layer 14, the etching stop layer 15, the second p-type cladding layer 16, the p-type contact layer 17, and the insulating layer 8 are sequentially formed.

  The red semiconductor laser element a and the infrared semiconductor laser element b are electrically separated by a separation groove 20 whose bottom reaches the substrate 1.

  The insulating layer 8 includes an upper surface of a ridge stripe portion having a trapezoidal cross section formed in the second p-type cladding layer 6 in the red semiconductor laser device a and a second p-type in the infrared semiconductor laser device b. Except for the top surface of the ridge stripe portion formed in the cladding layer 16, the top surfaces of the etching stop layers 5 and 15 and the side surfaces of the ridge stripe portions are covered.

  A p-side electrode 9 is formed on the upper surface of the ridge stripe portion in the red semiconductor laser device a, and carriers (holes) are injected into the active layer 3 from the ridge stripe portion. Similarly, a p-side electrode 19 is formed on the upper surface of the ridge stripe portion in the infrared semiconductor laser element b, and carriers (holes) are injected into the active layer 13 from the ridge stripe portion.

  An n-side electrode 10 is formed on the surface of the substrate 1 opposite to the p-side electrodes 9 and 19. Therefore, by independently applying a bias voltage to each of the p-side electrodes 9 and 19 and the n-side electrode 10, the semiconductor laser elements a and b can be operated independently.

  The two opposing end faces of the resonator formed below each ridge stripe portion are coated with a dielectric reflecting film 30 on the emitting end face and a dielectric reflecting film 31 on the rear end face, each made of a dielectric. The dielectric reflecting film 30 on the emission end face forms an emission end face (front end face) 40 on the end face from which the laser light is emitted, and is located on the opposite side of the emission end face 40 to the end face on which the laser light is reflected. A rear end face (reflection end face) 41 is formed.

  Here, each of the dielectric reflection films 30 and 31 is composed of a plurality of dielectric films having different refractive indexes, and a desired reflectance is obtained by adjusting the refractive index, the film thickness, and the number of layers of each dielectric reflection film. be able to.

  Each ridge stripe portion is not limited to a trapezoidal cross section, and may have a rectangular cross section whose side surface is substantially perpendicular to the substrate surface.

A typical method for forming the dielectric reflection film is an ECR (Electron Cyclotron Resonance) sputtering method. The reason why the ECR plasma processing apparatus is used is that it has characteristics such as low gas pressure (10 ⁻⁴ to 10 ⁻⁵ Torr), low plasma damage, and low ion damage. For film formation, Al ₂ O ₃ , SiO ₂ because various thin films such as SiN can be formed densely and with high quality at low temperatures without heating.

The dielectric reflecting film 31 on the rear end face preferably has a reflectivity of 90% or higher, and a high reflectivity can be achieved by taking a multilayer structure of a low refractive index material and a high refractive index material. For example, SiO ₂ (refractive index 1.48) is used as the low refractive index material, and hydrogenated amorphous Si (real part n = 3.3 of the refractive index) is used as the high refractive index material.

The dielectric reflective film 30 of the light emitting face _{40, SiO 2, Al 2 O} 3, Ta 2 O 5, Nb 2 O 5, ZrO 2 and the like are used. By combining the dielectric materials and setting the film thickness accurately, it is possible to realize a low reflectance coat corresponding to multiple wavelengths. Here, SiO ₂ is excellent in chemical stability, heat resistance, light transmission, and electrical insulation, and is often used as an optical dielectric reflecting film. However, when the laser is operated at a high output, COD (instantaneous optical damage) due to deterioration of the end face occurs as a problem. This is considered to be caused by a high concentration level of SiO ₂ impurities (mainly heavy metal elements such as Fe, Cr, Ni) deposited by the sputtering method. When high-power laser operation is performed with a dielectric reflection film having a high impurity concentration level in direct contact with the output end face, a deep level is generated at the output end face due to the mixing of heavy metal impurities, and no light is emitted through the deep level. It is considered that the end face temperature is increased due to recombination and the end face is deteriorated. Therefore, it is expected that the reliability of the high-power semiconductor laser device can be improved by forming a dielectric reflection film having a low heavy metal impurity concentration level on the first dielectric film in contact with the emission end face. As a dielectric material having a low impurity concentration level, there is Al ₂ O ₃ . Since Al ₂ O ₃ has a higher barrier property against impurity elements than SiO ₂ , it is known that the concentration of impurities such as Fe, Cr, and Ni contained in the film is low. Therefore, a reliability test was performed by using Al ₂ O ₃ for the first dielectric film and changing the impurity concentration at the interface, and the above contents were verified.

In the above verification, the first dielectric film on the emission end face 40 side is made of Al ₂ O ₃ and the second dielectric film is made of SiO ₂ , and the reflectivity with respect to the red semiconductor laser element a and the infrared semiconductor laser element b respectively. The film thickness is set so as to be between 1 and 7%.

  FIG. 2 shows the verification result. This shows the relationship between the heavy metal impurity concentration at the interface between the emission end face and the first dielectric film and the lifetime of the element in the red semiconductor laser element, and Fe is attracting attention as a heavy metal. The high output is, for example, the optical output 240 mW class.

FIG. 2 shows that there is a clear correlation between the impurity concentration and the lifetime (reliability) during high output operation. In order to realize a lifetime of 1000 hours or more, it is necessary that the heavy metal impurity concentration at the interface between the emission end face and the first dielectric film be 3 × 10 ¹⁷ atoms / cm ³ or less.

  As described above, in order to realize further higher output and longer life, it is not sufficient to prevent oxidation of the emission end face of the semiconductor laser, and it is also essential to reduce the contamination level of heavy metal impurities.

The present inventor has studied the optical output of a semiconductor laser device having a heavy metal impurity concentration of 3 × 10 ¹⁷ atoms / cm ³ or less. FIG. 3 shows the light intensity distribution inside the resonator. Here, the reflectance of the emission end face 40 is 6%, the reflectance of the rear end face 41 is 96%, and the resonator length is 1500 μm. In the semiconductor laser device operating at 240 mW output, reliability of a lifetime of 1000 hours or more is obtained, but at the time of 300 mW output operation, deterioration occurs from the rear end face 41. With reference to the light intensity at the rear end face 41 when this deterioration occurs, the result of estimating the light density at the end face of the semiconductor laser by simulation is 23.6 MW / cm ² .

  The dielectric reflection film having a low contamination level of heavy metal can be obtained by protecting the metal surface inside the ECR plasma processing apparatus and suppressing contamination due to metal surface sputtering.

  FIG. 4 shows a cross-sectional view of a typical ECR sputtering apparatus. This apparatus includes a plasma generation chamber 51 that generates ECR plasma, a microwave supply means 52 that supplies microwaves to the plasma generation chamber 51, and a film formation chamber (sputter chamber) 53 that communicates with the plasma generation chamber 51. I have.

The plasma generation chamber 51 has openings coaxially formed at the upper end and the lower end, and the microwave supply means supplies a microwave having a frequency of 2.45 GHz to the lower end through the lower end opening while maintaining the degree of vacuum. 52 and a gas introduction pipe 54 for introducing an argon (Ar) gas as a sputtering gas and a cleaning gas and an oxygen (O ₂ ) gas as a reactive gas. A magnetic coil 55 for generating a magnetic field that satisfies the ECR condition is provided around the plasma generation chamber 51.

  The film formation chamber 53 is connected to the upper end opening of the plasma generation chamber 51 at the lower end opening, and an exhaust port 53a for evacuating the chamber is open to the side wall. In the film forming chamber 53, a target material 56 such as Si or Al provided at the upper end of the plasma generating chamber 51 so as to surround the upper end opening is installed so as to cover the inner wall facing the lower end opening. A stage 57 for installing a substrate m as a film formation target is provided so as to face the lower end opening. The target material 56 is connected to an RF power source E for applying a negative bias voltage.

  FIG. 5 is an enlarged view of the microwave supply means 52 connected to the plasma generation chamber 51. As shown in FIG. 5A, the microwave source 58 is connected to the plasma generation chamber 51 via a rectangular waveguide 59a, a matching unit 60, rectangular waveguides 59b and 59c, and a vacuum waveguide 61. . The rectangular waveguide 59c branches the microwave into two, and is an E-plane Y branch circuit in the microwave circuit. The vacuum waveguide 61 has a slit 62 for sending out a microwave at the center, and as shown in FIG. 5B, the microwave makes the microwave electric field parallel to the external magnetic field and is perpendicular to the external magnetic field. And a tapered tube portion 61b that guides the microwave to the plasma generation chamber 51 along an external magnetic field. The slit 62 is short in the microwave traveling direction (longitudinal direction of the waveguide portion 61a) in the waveguide portion 61a and has a rectangular opening that is long in a direction perpendicular thereto, and the plasma generation chamber 51 side of the tapered tube portion 61b is A circular microwave introduction opening 63 having a diameter equal to the longitudinal direction of the slit 62 is formed.

  Microwave introduction windows 64a and 64b for introducing a microwave while maintaining a vacuum are provided at symmetrical positions on both sides of the slit 62, where the microwave proceeds perpendicularly to the external magnetic field. In this example, a quartz plate is used.

  With such a configuration, the microwave from the microwave source 58 is guided to the rectangular waveguide 59c which is a branch circuit through the rectangular waveguide 59a, the matching unit 60, and the rectangular waveguide 59b, and is branched into two there. After traveling at the same propagation distance, they pass through the microwave introduction windows 64a and 64b and reach the slit 62. At this time, the phases of the two microwaves branched by the rectangular waveguide 59c are different from each other by 180 degrees. Therefore, in the vicinity of the slit 62, the microwaves from the microwave introduction window 64a and the microwave introduction window 64b The microwaves cancel each other out to form a standing wave node, and the microwave electric field strength becomes very weak, so that plasma generation in the waveguide portion 61a is prevented. On the other hand, since the high-frequency current flowing through the waveguide wall is cut off by the slit 62, the microwave reaching the slit 62 is radiated into the tapered tube portion 61 b and further radiated into the plasma generation chamber 51.

  As a result of the microwaves radiated into the plasma generation chamber 51 in this way, the gas introduced from the gas introduction tube 54 is excited and turned into plasma, and the plasma flows into the film formation chamber 53 to sputter the target material 56. A thin film of the target material 56 is formed on the substrate m.

  At this time, since the microwave introduction windows 64a and 64b are at the blind spot as viewed from the microwave introduction opening 63, the particles in the plasma generated in the plasma generation chamber 51 do not fly directly, The adhesion of the film to the microwave introduction windows 64a and 64b is prevented.

The plasma processing apparatus using ECR plasma to form a thin film as a low gas pressure (10 ^-4 ~10 ^-5 Torr), a low plasma damage, has features such as low ionic damage, Al ₂ Various thin films such as O ₃ , SiO ₂ and SiN can be formed densely and with high quality at a low temperature without heating.

  In the plasma processing apparatus described above, the plasma generation chamber 51 includes a quartz tube 65, a quartz plate 66 having a circular opening serving as a plasma extraction window, and a quartz plate 67 having a square opening serving as a microwave introduction window. This prevents the heavy metal element from flying to the substrate m.

However, in the plasma processing apparatus, in general, a part of the plasma generated in the plasma generation chamber 51 spreads to the microwave supply means 52 side, so that the connection portion, in the above-described example, the metal surface of the opening of the microwave rectifying plate 68 is formed. Sputtering causes scattering of metal elements and flying onto the substrate m. Therefore, it is difficult to suppress the heavy metal contamination amount of the film formed on the substrate m to 3 × 10 ¹⁷ atoms / cm ³ or less.

Therefore, the metal inner wall facing the communication opening with the plasma generation chamber 51 is covered with a plasma-resistant protective material, so that the scattering of metal elements from the metal inner wall is suppressed, and the film formed in the film formation chamber 53 The metal contamination level can be reduced to 3 × 10 ¹⁷ atoms / cm ³ or less.

  The dielectric reflection film of the semiconductor laser device can be deposited not only by the ECR sputtering method but also by magnetron sputtering, electron beam evaporation (EB evaporation) or the like. Also in these deposition methods, a dielectric reflection film with a reduced metal contamination level may be formed by protecting the contamination source inside the sputtering apparatus with a protective film having excellent durability and suppressing the sputtering of the metal surface. .

Furthermore, as the first dielectric film in contact with the emission end face, it is desirable to employ an Al ₂ O ₃ film having a lower impurity concentration level than SiO ₂ and excellent in heat dissipation.

Thus, according to the present embodiment, the heavy metal impurity concentration at the interface between the emission end face and the dielectric reflecting film is formed to be 3 × 10 ¹⁷ atoms / cm ³ or less, which is suitable for high output operation and reliable. A highly integrated semiconductor laser device can be obtained.

  The integrated semiconductor laser device of the present invention is useful, for example, as a light source for an optical recording device or the like that requires a high-power two-wavelength laser device, and is also useful for other applications such as laser medicine.

1 is a perspective view of an integrated semiconductor laser device (dual wavelength type) according to an embodiment of the present invention. The figure which shows the relationship between the impurity concentration of Fe contained in the output end surface of the semiconductor laser apparatus in embodiment of this invention, and lifetime. The figure which shows light intensity distribution inside the resonator of the red semiconductor laser element in embodiment of this invention Sectional drawing which shows the ECR plasma processing apparatus in embodiment of this invention FIG. 4 is an enlarged cross-sectional view of the microwave introduction portion of FIG. Perspective view and cross-sectional view of a conventional semiconductor device (two-wavelength type)

Explanation of symbols

a red semiconductor laser device b infrared semiconductor laser device 1 n-type GaAs substrate 2 n-type cladding layer 3 active layer 4 first p-type cladding layer 5 etching stop layer 6 second p-type cladding layer 7 p-type contact layer 8 Insulating layer 9 p-side electrode 10 n-side electrode 12 n-type cladding layer 13 active layer 14 first p-type cladding layer 15 etching stop layer 16 second p-type cladding layer 17 p-type contact layer 19 p-side electrode 20 separation groove DESCRIPTION OF SYMBOLS 30 Dielectric reflecting film of output end face 31 Dielectric reflecting film of rear end face 40 Outgoing end face 41 Back end face

Claims (9)

A dielectric reflection film having a single-layer structure or a multi-layer structure is formed on the emission end face of the laser beam, and heavy metal impurities in the first dielectric film in contact with the emission end face and at the interface between the first dielectric film and the emission end face A semiconductor laser device whose concentration is set to 3 × 10 ¹⁷ atoms / cm ³ or less.   The semiconductor laser device according to claim 1, wherein the heavy metal impurity element includes at least one element selected from the group consisting of Fe, Cr, and Ni. The dielectric reflection film includes the first dielectric film in contact with the emission end face and a second dielectric film formed outside the first dielectric film, and the refractive index n ₁ of the first dielectric film. The semiconductor laser according to claim 1, wherein 1.6 ≦ n ₁ ≦ 2.3, and the refractive index n ₂ of the second dielectric film is 1.4 ≦ n ₂ <1.6. apparatus. The first dielectric film is at least one compound selected from the group consisting of Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and ZrO ₂ , and the second dielectric film is SiO _2. The semiconductor laser device according to any one of claims 1 to 3.   The semiconductor laser device according to any one of claims 1 to 4, wherein a reflectance at the emission end face is set in a range of 1 to 7%. 7. The semiconductor laser device according to claim 1, wherein the light density at the emission end face is set to 23.6 MW / cm ² or more.   7. The semiconductor laser device according to claim 1, wherein the oscillation wavelength is a single wavelength.   7. An integrated semiconductor laser device according to claim 1, wherein a plurality of semiconductor laser devices having different oscillation wavelengths are formed on the same substrate.   There are two semiconductor laser devices, and the first semiconductor laser device having a shorter oscillation wavelength has an active layer material of the semiconductor laser made of an AlGaInP-based semiconductor material, and the second semiconductor laser device having a longer oscillation wavelength. 9. The integrated semiconductor laser device according to claim 8, wherein the active layer material is an AlGaAs-based semiconductor material.

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