JP2008153703A - Gallium nitride semiconductor laser device - Google Patents

Abstract

In a nitride-based compound semiconductor laser device, it has been difficult to manufacture a gallium nitride-based semiconductor laser device having an optical waveguide structure having a favorable refractive index distribution and a high efficiency and a high production yield.
According to the present invention, in a gallium nitride semiconductor laser device having a substrate, a lower cladding layer, an active layer, and an upper cladding layer in this order, the upper cladding layer extends in the cavity direction. And a gallium nitride based semiconductor laser device, wherein a p-type electrode is formed on the upper surface of the ridge stripe.
[Selection] Figure 1

Description

  The present invention relates to a gallium nitride based semiconductor laser device.

  Gallium nitride-based compound semiconductors are wide-gap semiconductors and have a direct transition type band structure, and thus are expected to be applied to light-emitting elements having emission wavelengths from blue to ultraviolet.

  Among these applications, double hetero-type light emitting diodes using GaInN as an active layer and GaAlN as a cladding layer have been put into practical use, and are being actively developed for practical use of semiconductor laser elements. Such a semiconductor laser device is manufactured by using a sapphire or SiC substrate by a metal organic chemical vapor deposition method (hereinafter referred to as MOCVD method) or a molecular beam epitaxial method (hereinafter referred to as MBE method). Schematic diagrams of a compound semiconductor laser device manufactured conventionally are shown in FIGS.

  In the compound semiconductor laser device shown in FIG. 10, a buffer layer 102 for lattice matching, a lower cladding layer 103, an active layer 104, and an upper cladding layer 105 are sequentially formed on a substrate 101. In the figure, reference numeral 106 denotes a current blocking layer, and 107 and 108 denote metal electrodes. In the compound semiconductor laser device shown in FIG. 10, current injection is performed by the metal electrode 108 in contact with the cladding layer 105 at the opening of the current blocking layer 106. In the element having such a structure, the current injected from the opening of the current blocking layer 106 spreads in the horizontal direction in the upper cladding layer 105, so that the current injection width in the active layer 104 is equal to the opening of the current blocking layer 106. It becomes wider than the width. Further, in this element structure, since a structure for confining light in the horizontal direction is not formed, an opening portion of the current blocking layer 106 is generated by a difference in gain generated in a portion where current is injected and a portion where current is not injected. An optical waveguide is formed in such a manner that the light intensity is concentrated below (hereinafter referred to as an electrode stripe structure).

  In the semiconductor laser device shown in FIG. 11, a buffer layer 152, a lower cladding layer 153, an active layer 154, an upper cladding layer 155, a current blocking layer 156, and a contact layer 157 are sequentially formed on a substrate 151. In the figure, reference numerals 158 and 159 denote metal electrodes. In the compound semiconductor laser device shown in FIG. 11, the current blocking layer 156 is placed in the semiconductor multilayer structure, and the current injection width is limited by this opening. Even in this case, the current spreads in the horizontal direction in the clad layer 155, but since the thickness of the clad layer 155 can be made thinner than in the case of FIG. 10, the spread of the current can be reduced. Furthermore, in the semiconductor laser device structure of FIG. 11, since the current blocking layer 156 is made of a material that absorbs light emitted from the active layer, the current blocking layer 156 has a lower portion and a lower portion other than the opening. A structure having a refractive index difference in the horizontal direction is formed, and an optical waveguide is formed (hereinafter referred to as an internal current confinement structure).

  However, the above-described conventional compound semiconductor laser device and manufacturing method have the following problems. In the compound semiconductor laser device having the electrode stripe structure as shown in FIG. 10, since the current spreading in the horizontal direction in the cladding layer 105 occurs as described above, the current injection efficiency into the active layer is poor and the oscillation threshold value is high. Furthermore, since an optical waveguide having a refractive index distribution in the horizontal direction is not built, the horizontal wavefront is greatly bent, the astigmatic difference is as large as several tens of μm, and good focusing characteristics cannot be obtained. There is a problem that it is not suitable for a light source of a pickup for an optical disk.

  On the other hand, in the case of a compound semiconductor laser device having an internal current confinement structure as shown in FIG. 11, the above-mentioned problem is solved. That is, the efficiency of current injection into the active layer 154 is good, the oscillation threshold value can be lowered, and an optical waveguide having a horizontal refractive index profile is built, so that the horizontal wavefront is small in bending and the astigmatic difference is small. Since it is as small as several μm and good focusing characteristics are obtained, it is suitable as a light source for optical disk pickups. Therefore, it is generally widely used in AlGaAs and AlGaInP infrared to red light emitting semiconductor lasers. It is well known.

  However, no suitable chemical etchant has been found for gallium nitride-based materials, and the current blocking layer necessary to fabricate the internal current confinement structure can be removed by wet etching to about 0.5 μm to 1 μm. It takes several tens of hours or more, and it is practically impossible to manufacture a compound semiconductor laser device having a structure as shown in FIG.

  In addition, when the dry etching method is used for the film thickness of a gallium nitride-based material, a practical etching of several thousand liters per minute is possible, but the variation in the dry etching rate within the wafer surface is ± It is as large as about 25%. Therefore, in the nitride compound semiconductor laser device having a standard structure as shown in FIG. 11 in which the thickness of the upper cladding layer 155 is 0.2 μm and the thickness of the current blocking layer 156 is 1 μm, the current blocking layer 156 is striped. At the interface between the contact layer 157 and the upper clad layer 155, a portion where the current blocking layer 156 is not completely etched away or a portion where the etching has progressed excessively to the upper clad layer 155 is removed. It occurs in the same plane. Therefore, in the gallium nitride-based compound semiconductor laser device having the structure of FIG. 11, defective current injection, crystal quality deterioration of the active layer, and the like occur.

  An object of the present invention is to provide a highly efficient gallium nitride-based compound semiconductor laser device having an optical waveguide structure having a refractive index distribution in the horizontal direction by solving the above problems.

  The nitride semiconductor laser device according to the present invention includes a substrate, a first conductivity type lower cladding layer, an active layer, a second conductivity type upper cladding layer, and a second conductivity type contact layer in this order. The gallium nitride based semiconductor laser has a ridge stripe extending in the cavity direction between the second conductive type upper cladding layer and the second conductive type contact layer, and a protective film is provided on a side surface of the ridge stripe. The p-type electrode is formed on the entire upper surface of the ridge stripe.

  The nitride semiconductor laser device according to the present invention includes a conductive substrate, a first conductive type lower cladding layer, an active layer, a second conductive type upper cladding layer, and a second conductive type contact layer. And the second conductive type upper cladding layer and the second conductive type contact layer have ridge stripes extending in the direction of the resonator, and a protective film is provided on a side surface of the ridge stripe. The p-type electrode is formed on the entire top surface of the ridge stripe, and the n-type electrode is formed on the back surface of the conductive substrate.

  Further, a protective film is provided on the surface of the second conductivity type upper clad layer having the ridge stripe shape.

  In the nitride semiconductor laser device according to the present invention, the first conductive type lower cladding layer is made of any one of AlGaN, GaN, and GaAlInN, the active layer is made of any of InGaN and GaN, The conductive type upper clad layer 2 is made of any one of AlGaN, GaN, and GaAlInN.

  In the nitride semiconductor laser device according to the present invention, the active layer is a single quantum well layer or a multiple quantum well layer made of InGaN.

  The gallium nitride-based compound semiconductor laser element as shown in the present embodiment is less likely to cause current injection defects due to etching variations and has a low oscillation threshold, unlike the conventional compound semiconductor laser element. The astigmatic difference was reduced.

  Further, the ridge stripe shape of the compound semiconductor laser can be produced by a dry etching method or a selective growth method. In particular, when the selective growth method is used, the film thickness controllability of the outer upper cladding layer in the ridge stripe shape is excellent, and the variation of the elements is improved. In addition, by providing a protective layer on the side surface where the interface between the contact layer and the upper cladding layer exists, it is possible to prevent the current injection path from deteriorating. Further, by forming the protective film of the upper cladding layer into two layers, The protective effect is high and the device life is improved.

(Embodiment 1)
As an embodiment according to the present invention, a method of manufacturing a compound semiconductor laser device having a double heterojunction having a GaInN active layer / GaAlN cladding layer on a SiC substrate and a ridge guide structure by using dry etching will be described. .

The structure of a gallium nitride based semiconductor laser device according to the present invention is shown in FIG. Reference numeral 1 denotes a 6H-SiC substrate, 2 denotes an AlN buffer layer, 3 denotes an n-type GaN layer, 4 denotes an n-type Ga _0.85 Al _0.15 N lower cladding layer, 5 denotes a Ga _0.75 In _0.25 N active layer, and 6 denotes a p-type Ga _0.85 An Al _0.15 N upper cladding layer, 7 is a p-type GaN contact layer, 9 is an Al ₂ O ₃ protective film, 10 is a p-side electrode, and 11 is an n-side electrode. (Hereinafter, in the form of this example, GaAlN and GaInN represent the above-mentioned composition.) Further, the symbol d indicates the film thickness of the p-type GaAlN upper cladding layer 6 outside the ridge stripe shape.

  The semiconductor laser element shown in FIG. 1 is characterized in that the upper clad layer forms a ridge stripe shape.

  FIG. 2 shows a cross-sectional view of a manufacturing process of a gallium nitride compound semiconductor laser according to the present invention. First, the damaged layer on the surface was removed by subjecting the 6H—SiC substrate 1 that was turned off 5 degrees in the <1120> direction from the n-type (0001) silicon (Si) surface as the substrate to an oxidation treatment after the surface polishing. . This 6H-SiC substrate was set in the reactor of the MOCVD apparatus, and the reactor was thoroughly replaced with hydrogen, and then the temperature was raised to 1500 ° C. while flowing hydrogen and ammonia and held for 10 minutes to clean the surface of the 6H-SiC substrate 1. Do.

Next, when the substrate temperature is lowered to 1050 ° C. and stabilized at 1050 ° C., 3 × 10 ⁻⁵ mol of trimethylaluminum (hereinafter referred to as TMA) is flowed at a rate of 5 liters per minute and ammonia is treated for 5 minutes. An AlN buffer layer 2 of about 0.1 μm is grown. A cross-sectional view after the above process is shown in FIG.

Next, 3 × 10 ⁻⁵ mol of trimethylgallium (hereinafter referred to as “TMG”) per minute, 5 liters of ammonia per minute, and 0.3 cc of silane gas as a Si doping material were allowed to flow for 15 minutes. An n-type GaN layer 3 for lattice matching is grown.

Next, in addition to ammonia and TMG, 6 × 10 ⁻⁶ mol of TMA per minute and 0.3 cc of silane gas are flowed per minute, and an n-type GaAlN lower cladding layer 4 of about 1 μm is grown by treatment for 25 minutes. The electron density of this layer is 2 × 10 ¹⁸ cm ⁻³ .

Next, the supply of TMG, TMA, and silane gas is stopped and the temperature is lowered to 800 ° C. When the temperature is stabilized at 800 ° C., TMG and trimethylindium (hereinafter referred to as TMI) are flowed at 4 × 10 ⁻⁴ moles per minute and treated for 12 seconds to grow a 10 nm GaInN active layer 5.

Next, the supply of TMG and TMI is stopped, and the temperature is raised to 1050 ° C. again. When the temperature is stabilized at 1050 ° C., Tg, TMA, and p-type doping material are supplied with Cp ₂ Mg (cyclopentadienylmagnesium) at a flow rate of 5 × 10 ⁻⁶ moles per minute and treated for 25 minutes to give about 1 μm Mg doped. The grown GaAlN upper cladding layer 6 is grown.

  Next, the supply of only TMA is stopped, and a 300 nm Mg-doped GaN contact layer 7 is grown for 7.5 minutes. A cross-sectional view after the above process is shown in FIG.

A stripe-like SiO ₂ film 8 having a width of 1 μm is formed on the Mg-doped GaN contact layer 7 of the semiconductor device manufactured as described above by an electron beam evaporation method and a photolithography process. A cross-sectional view after the above process is shown in FIG.

Next, the reactive ion etching apparatus is used to etch the Mg-doped GaN layer contact layer 7 and the Mg-doped GaAlN upper clad layer 6 other than the stripe-shaped SiO ₂ film 8 forming portion with an etching gas containing chlorine as a main component. Went. In this etching step, the etching time is adjusted so that the Mg-doped GaAlN upper clad layer 6 is 0.2 μm and the etching is completed. Here, by setting the DC bias to 200 V and the RF power 300 W as the etching conditions, the etching rate of both the Mg-doped GaN layer contact layer 7 and the Mg-doped GaAlN upper cladding layer 6 is 3000 Å / min, and the etching is about 4 minutes. It went for 20 seconds. Under the above conditions, the DC bias was ± 50 V, the RF power was ± 50 W, and the variation in the etching rate was about ± 10%.

Next, a heat treatment at about 700 ° C. is performed in a nitrogen atmosphere for about 20 minutes, and the Mg-doped GaAlN upper cladding layer 6 and the GaN contact layer 7 are reduced in resistance and p-type. This treatment resulted in a hole concentration of both layers of about 1 × 10 ¹⁸ cm ⁻³ . A cross-sectional view after the above process is shown in FIG.

Next, an Al ₂ O ₃ film 9 is formed as a protective film on the side surface of the ridge stripe shape by an electron beam evaporation method, and then the striped SiO ₂ film 8 having a width of 1 μm is removed with hydrofluoric acid, washed sufficiently with water, and dried. After performing the above, the p-side electrode 10 of the Au / Ni laminated film is formed entirely on the upper surface of the ridge type stripe by the vacuum evaporation method.

Next, the mirror surface of the laser resonator is formed. Electron beam deposition is performed by using a SiO ₂ film having a width of 500 μm with a spacing of 50 μm as a mask in a direction perpendicular to the electrode stripe formed by the Au / Ni laminated film 10.

Next, the wafer on which the SiO ₂ film having a 50 μm stripe is formed is introduced into a reactive ion etching apparatus, and the gallium nitride based semiconductor layer in the opening of the SiO ₂ film is formed on the AlN buffer layer 2 to form a reflection mirror. Etching is removed by the usual reactive ion beam etching method. Further, the 6H—SiC substrate 1 is polished and processed to a thickness of about 100 μm, and the SiO ₂ film used as a mask is removed.

  Next, n-side electrode 11 is formed on the entire back surface of SiC substrate 1. Through the above steps, a GaAlInN-based semiconductor laser element is formed. A cross-sectional view after the above process is shown in FIG.

  Finally, it is divided into chips by scribing and mounted on a package by a normal method to complete the laser element.

  FIG. 5 shows the correlation between the upper cladding layer thickness d outside the ridge stripe shape and the horizontal radiation angle. It can be seen that the horizontal radiation angle characteristic increases rapidly as the thickness d of the upper cladding layer decreases. FIG. 5 shows that the spread of the horizontal radiation angle can be suppressed when the thickness d of the upper cladding layer is larger than 0.2 μm.

  In an element manufactured by the manufacturing method using dry etching shown in the first embodiment, laser oscillation is typically observed at a current of 50 mA, and the radiation angle characteristics include a vertical divergence angle of 24 ° and a horizontal direction. The characteristic of ellipticity 2 with a divergence angle of 12 ° was obtained, but the oscillation threshold was in the range of 30 mA to 100 mA, and the divergence angle in the horizontal direction was in the range of 10 ° to 23 °. The astigmatic difference was 1 to 5 μm.

  In the present embodiment, an example of a blue light emitting semiconductor laser element using a GaInN layer as an active layer and GaAlN as a cladding layer is shown. However, the present invention is not limited to this combination, and a GaInN active layer / GaN cladding layer or GaN active layer is used. A layer / GaAlN cladding layer, or a combination of GaAlInN-based quaternary compounds as long as the combination is capable of laser oscillation.

(Embodiment 2)
FIG. 3 shows a blue-emitting compound semiconductor laser device manufactured by a selective growth method to form a ridge stripe shape. The same members as those in FIG. Reference numeral 21a is a p-type GaAlN upper cladding layer, 21b is a selectively grown p-type GaAlN upper cladding layer, and 23 is a SiO ₂ protective film. This compound semiconductor laser element has a ridge stripe shape, and further has a protective film comprising two layers of silicon oxide and aluminum oxide on the surface of the ridge stripe-shaped p-type GaAlN upper cladding layer.

Next, a method for manufacturing the compound semiconductor laser device of the second embodiment will be described.
First, fabrication is performed in the same manner as in FIG. This process is shown in FIG.

Next, as in the first embodiment, an n-type GaN layer 3, an n-type GaAlN lower cladding layer 4, and a GaInN active layer 5 are stacked, the temperature is set to 1050 ° C., ammonia is 5 liters per minute, and TMG is 3 minutes per minute. × 10 ^-5 mol, TMA per minute 6 × 10 ^-6 mol and Cp ₂ Mg is flowed min 5 × 10 ^-6 mol, a GaAlN upper cladding layer 21a that Mg-doped 0.2μm by treating 5 min Grow. The above process is shown in FIG.

Next, an SiO ₂ film 23 having an opening 22 having a width of 1 μm is formed on the surface of the Mg-doped GaAlN upper clad layer 21a by electron beam evaporation and photolithography. The above process is shown in FIG.

Thereafter, a wafer in which a double heterostructure made of a gallium nitride compound semiconductor formed with an SiO ₂ film 23 having an opening 22 having a width of 1 μm was introduced into the MOCVD apparatus, and the reactor of the MOCVD apparatus was sufficiently replaced with hydrogen. Then, the temperature was raised to 1050 ° C. while flowing hydrogen and ammonia, and when the temperature was stabilized at 1050 ° C., 3 × 10 ⁻⁵ mol / min of TMG, 6 × 10 ⁻⁶ mol / min of TMA, and Cp ₂ Mg / min An about 0.8 μm Mg-doped GaAlN upper cladding layer 21 b is grown in the opening 22 having a width of 1 μm by flowing 5 × 10 ⁻⁶ mol per minute and 5 liters of ammonia per minute and treating for 20 minutes. Since this growth is selectively performed only in the opening 22, the semiconductor layer does not grow on the SiO ₂ film 23 other than the opening 22.

Next, the supply of only TMA is stopped, and a 0.5 μm Mg-doped GaN contact layer 7 is grown for 10 minutes. As described above, a portion other than the SiO ₂ film 23 is selectively grown to form a ridge stripe shape serving as an optical waveguide. A cross-sectional view after the above steps are shown in FIG.

Next, a heat treatment at about 700 ° C. is performed for about 20 minutes in a nitrogen atmosphere, and the Mg-doped GaAlN upper cladding layers 21a and 21b and the GaN contact layer 7 are reduced in resistance and p-type. With this treatment, the hole concentration in both layers was about 1 × 10 ¹⁸ cm ⁻³ .

Next, an Al ₂ O ₃ film 9 is formed as a protective film on the surface other than the upper surface of the ridge stripe shape by an electron beam evaporation method using a normal photolithography method, and the Au / Ni laminated film is formed only on the upper surface of the ridge stripe shape. The p-side electrode 10 is entirely formed by vacuum deposition. A cross-sectional view after the above process is shown in FIG. The surface protection of the p-type GaAlN upper cladding layer can be simplified to a two-layer structure by leaving the SiO ₂ film used for selective growth and laminating the Al ₂ O ₃ film 9 thereon.

Next, the mirror surface of the laser resonator is formed. Electron beam deposition is performed on a SiO ₂ film having a width of 500 μm with an interval of 50 μm as a mask in a direction perpendicular to the electrode stripe formed by the Au / Ni laminated film 10.

Next, the wafer on which the SiO ₂ film having a 50 μm stripe is formed is introduced into a reactive ion etching apparatus, and the GaAlInN-based semiconductor layer in the opening of the SiO ₂ film is formed up to the AlN buffer layer 2 in order to form a reflection mirror. Etching is removed by a normal reactive ion beam etching method. Further, the 6H—SiC substrate 1 is polished and processed to a thickness of about 100 μm, and the SiO ₂ film used as a mask is removed.

  Finally, an n-side electrode 11 is formed on the entire back surface of the SiC substrate 1, divided into chips by scribing, and mounted on a package by a normal method to complete a nitride-based laser device.

  When a current was passed through the compound semiconductor laser device manufactured using the selective growth method, laser oscillation at a blue wavelength of 432 nm was typically observed with a threshold current of 40 mA, and the radiation angle characteristics were A characteristic of ellipticity 2 with a vertical divergence angle of 24 ° and a horizontal divergence angle of 12 ° was obtained. The astigmatic difference was 1 to 5 μm.

  In the element manufactured in this embodiment, the oscillation threshold is 38 mA to 42 mA, and the horizontal divergence angle is in the range of 11.5 ° to 12.5 °. Compared with the characteristics of the first embodiment, It was shown that the cladding layer thickness control outside the ridge stripe is excellent. The film thickness controllability of the GaAlN cladding layer by the MOCVD method was about ± 2% in the φ2 inch substrate surface.

  In the compound semiconductor laser device shown in the second embodiment, the protective film of the upper clad layer outside the ridge stripe has two layers of aluminum oxide and silicon oxide, so that the protective effect is high and the device life is long. Improved.

  In this embodiment, the example in which the 6H—SiC substrate 1 that is turned off by 5 degrees in the <1120> direction from the n-type (0001) silicon (Si) plane is described as the substrate. However, a p-type SiC substrate is used. In this case, it is necessary to reverse the conductivity type of each semiconductor layer described in the embodiment. The same effect was obtained even when a substrate that was not turned off was used. Further, not only 6H—SiC but also a 4H—SiC substrate and a 2H—SiC substrate can provide the same or higher effect.

  The ridge stripe shape does not need to be formed from the upper clad layer, and substantially the same effect can be obtained even if only the contact layer is formed into the ridge stripe shape.

(Embodiment 3)
FIG. 6 shows a blue-emitting compound semiconductor laser device formed on an insulating substrate using a selective growth method to form a ridge stripe shape as in the second embodiment. The same members as those in FIGS. 1 and 3 are denoted by the same reference numerals. Reference numeral 55 denotes a single quantum well structure GaInN active layer, 101 denotes an insulating substrate, and 102 denotes a GaN buffer layer. This compound semiconductor laser device has a ridge stripe shape, and further has a protective film formed of two layers of silicon oxide and aluminum oxide on the surface of the p-type GaAlN upper clad layer in the ridge stripe shape. This is the same as the second embodiment.

Next, a method for manufacturing the compound semiconductor laser device of the third embodiment will be described.
First, fabrication is performed in the same manner as in FIG. 4A of the second embodiment. This process is shown in FIG.

Next, as in the second embodiment, an n-type GaN layer 3, an n-type GaAlN lower cladding layer 4, and a single quantum well structure GaInN active layer 55 (20Å) are stacked, and the temperature is set to 1050 ° C. and ammonia is added every minute. 5 liters, TMG 3 × 10 ⁻⁵ mol / min, TMA 6 × 10 ⁻⁶ mol / min and Cp ₂ Mg flow 5 × 10 ⁻⁶ mol / min and treated for 11 minutes to give 0.43 μm Mg A doped GaAlN upper cladding layer 21a is grown. A cross-sectional view after the above steps are shown in FIG.

Next, an SiO ₂ film 23 having an opening 22 having a width of 1 μm is formed on the surface of the Mg-doped GaAlN upper clad layer 21a by electron beam evaporation and photolithography. FIG. 7C shows a cross-sectional view after completion of the above steps.

After that, a wafer on which a double heterostructure made of a gallium nitride compound semiconductor having an SiO ₂ film 23 having an opening 22 having a width of 1 μm is stacked is used as an MOCVD apparatus, and the reactor is sufficiently replaced with hydrogen. the temperature was raised to 1050 ° C. while flowing, the temperature is stabilized min 3 × 10 ^-5 mol of TMG After the 1050 ° C., min 6 × 10 ^-6 mol of TMA, Cp ₂ Mg per minute 5 × 10 ^{- An} about 0.8 μm Mg-doped GaAlN upper cladding layer 21b is grown in the opening 22 having a width of 1 μm by flowing ⁶ mol of ammonia at a rate of 5 liters per minute and treating for 20 minutes. Since this growth is selectively performed only in the opening 22, the semiconductor layer does not grow on the SiO ₂ film 23 other than the opening 22.

Next, the supply of only TMA is stopped, and a 0.5 μm Mg-doped GaN contact layer 7 is grown for 10 minutes. As described above, a portion other than the SiO ₂ film 23 is selectively grown to form a ridge stripe shape serving as an optical waveguide. FIG. 7D shows a cross-sectional view after the above steps are completed.

Next, a heat treatment at about 700 ° C. is performed for about 20 minutes in a nitrogen atmosphere, and the Mg-doped GaAlN upper cladding layers 21a and 21b and the GaN contact layer 7 are reduced in resistance and p-type. With this treatment, the hole concentration in both layers was about 1 × 10 ¹⁸ cm ⁻³ .

Next, an Al ₂ O ₃ film 9 is formed as a protective film on the entire wafer surface by an electron beam evaporation method using a normal photolithography method, and the Al ₂ O ₃ film 9 and the SiO _{2 in} portions other than the ridge stripe shape are formed. The film 23 is removed in a stripe shape, and an opening 222 is provided. FIG. 7E shows a cross-sectional view after completion of the above steps.

Next, the wafer in which the opening 222 is formed is introduced into a reactive ion etching apparatus, and the Al ₂ O ₃ film 9 and the gallium nitride based semiconductor layer in the opening of the SiO ₂ film 23 are formed in order to form an n-side electrode. Are removed by etching up to the n-type GaN layer 3 by an ordinary reactive ion beam etching method. FIG. 7F shows a cross-sectional view after the above steps are completed.

  Next, the n-side electrode 11 is formed on the surface of the n-type GaN layer 3 by using a normal photolithography method.

  Next, the p-side electrode 10 of the Au / Ni laminated film is formed entirely on the upper surface of the ridge stripe shape by a vacuum deposition method using a normal photolithography method.

Next, the mirror surface of the laser resonator is formed. Electron beam deposition is performed on a SiO ₂ film having a width of 500 μm with an interval of 50 μm as a mask in a direction perpendicular to the electrode stripe formed by the Au / Ni laminated film 10.

Next, the wafer on which the SiO ₂ film having a 50 μm stripe is formed is introduced into a reactive ion etching apparatus, and the gallium nitride based semiconductor layer in the opening of the SiO ₂ film is formed on the AlN buffer layer 2 to form a reflection mirror. Etching is removed by the usual reactive ion beam etching method. Further, the insulating substrate 101 is polished and processed to a thickness of about 100 μm, and the SiO ₂ film used as a mask is removed.

  Finally, it is divided into chips by scribing and mounted on a package by a normal method to complete the laser element.

  When a current is passed through a compound semiconductor laser device having a single quantum well structure active layer manufactured using the selective growth method, laser oscillation at a blue wavelength of 420 nm is typically performed with a threshold current of 30 mA. As a radiation angle characteristic, an ellipticity 2 characteristic with a vertical spread angle of 20 ° and a horizontal spread angle of 10 ° was obtained. The astigmatic difference was 1 to 5 μm.

  In the element manufactured in this embodiment, the oscillation threshold is 28 mA to 32 mA, and the horizontal divergence angle is in the range of 9.5 ° to 10.5 °. Compared with the characteristics of the second embodiment. It was also shown that the property controllability is further excellent.

  The compound semiconductor laser device shown in the third embodiment also has a high protective effect and a long device life because the protective film of the upper cladding layer on the outer side of the ridge stripe has two layers of aluminum oxide and silicon oxide. Improved.

  In the present embodiment, an element having an active layer having a single quantum well structure has been described. However, a quantum well has a plurality of multiple quantum well structures, for example, three InGaN layers having a thickness of 20 mm as well layers, The barrier layer may be an element structure having a structure in which two GaN layers having a thickness of 30 mm are alternately stacked. In the case of a multiple quantum well structure, the number of quantum wells is desirably 3 or less in consideration of good carrier injection into each quantum well layer and reduction in driving voltage.

(Embodiment 4)
FIG. 9 shows a blue-emitting compound semiconductor laser having a single quantum well structure GaInN active layer formed on a conductive substrate using dry etching to form a ridge stripe shape as in the first embodiment. An element is shown. The same members as those in FIG. 1, FIG. 3 and FIG.

  The manufacturing method of the compound semiconductor laser device of the fourth embodiment is the same as that of the first embodiment, but the manufacturing method of the first embodiment is only in that the single quantum well structure GaInN active layer 55 is stacked. Is different.

Next, the reactive ion etching apparatus is used to etch the Mg-doped GaN layer contact layer 7 and the Mg-doped GaAlN upper clad layer 6 other than the stripe-shaped SiO ₂ film 8 forming portion with an etching gas containing chlorine as a main component. In the case of the first embodiment, the etching time is adjusted in this etching step so that the Mg-doped GaAlN upper clad layer 6 is completely etched leaving 0.43 μm. Is different. Here, when the DC bias is 200 V and the RF power is 300 W as the etching conditions, the etching rate for both the GaN layer contact layer 7 and the Mg-doped GaAlN upper cladding layer 6 is 3000 Å / min, and the etching is performed for about 3 minutes and 25 seconds. It was. Under the above conditions, the DC bias was ± 50 V, the RF power was ± 50 W, and the variation in the etching rate was about ± 10%.

Next, heat treatment at about 700 ° C. in a nitrogen atmosphere was performed in the same manner as in the first embodiment.
Further, the steps of forming the p-side electrode 10 of the Au / Ni laminated film on the upper surface of the ridge-type stripe, forming the mirror surface of the laser resonator, and forming the n-side electrode 11 on the entire back surface of the SiC substrate 1 are also described in the first embodiment. As well as.

  Finally, it is divided into chips by scribing and mounted on a package by a normal method to complete the laser element.

  The characteristics of the element manufactured by the dry etching manufacturing method shown in the fourth embodiment were the same as those in the third embodiment.

  In the present embodiment, an example of a blue light emitting semiconductor laser element using a GaInN layer as an active layer and GaAlN as a cladding layer is shown. However, the present invention is not limited to this combination, and a GaInN active layer / GaN cladding layer or GaN active layer is used. As in the case of the first embodiment, a combination of a layer / GaAlN cladding layer or a combination of GaAlInN-based quaternary compounds may be used as long as the combination is capable of laser oscillation.

  Further, in the present embodiment as well as the third embodiment, the description has been made on the element having the active layer having the single quantum well structure. However, the element structure having the multiple quantum well structure in which a plurality of quantum wells exist may be used. In the case of a multiple quantum well structure, the number of quantum wells is preferably 3 or less in consideration of good carrier injection into each quantum well layer and reduction in driving voltage. It is the same.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a cross-sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in Embodiment 1 of the present invention. 6 is a diagram showing a manufacturing process of the gallium nitride based semiconductor laser device having the ridge stripe shape shown in the first embodiment. FIG. 4 is a cross-sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in Embodiment 2. FIG. FIG. 10 is a diagram showing a manufacturing process of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in the second embodiment. It is a figure which shows the relationship between the upper cladding layer thickness of the outer side of a ridge stripe shape, and a horizontal radiation angle. 6 is a cross-sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in Embodiment 3. FIG. FIG. 10 is a diagram showing a manufacturing process of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in the third embodiment. It is a figure which shows the relationship between the upper cladding layer thickness of the outer side of a ridge stripe shape in a device with a single quantum well active layer structure, and a horizontal radiation angle. 6 is a cross-sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in Embodiment 4. FIG. It is sectional drawing of the semiconductor laser element which has the conventional electrode stripe structure. It is sectional drawing of the semiconductor laser element which has the conventional internal current confinement structure.

Explanation of symbols

16 H-SiC substrate, 101 insulating substrate, 2 AlN buffer layer, 102 GaN buffer layer, 3 n-type GaN layer, 4 n-type GaAlN lower cladding layer, 5 InGaN active layer, 55 single quantum well structure InGaN active layer, 6 p-type GaAlN upper clad layer, 7 p-type GaN contact layer, 8 SiO ₂ film, 9 Al ₂ O ₃ protective film, 10 p-side electrode, 11 n-side electrode, 21 a p-type GaAlN upper clad layer, 21 b P-type GaAlN upper cladding layer, 22, 222 openings, 23 SiO ₂ film.

Claims (2)

  In a gallium nitride based semiconductor laser device having a substrate, a lower cladding layer, an active layer, and an upper cladding layer in this order, the upper cladding layer has a ridge stripe shape extending in the cavity direction, and a p-type electrode is A gallium nitride based semiconductor laser device formed on the upper surface of a ridge stripe.   2. The gallium nitride semiconductor laser device according to claim 1, wherein the gallium nitride semiconductor laser device is a semiconductor laser for a light source of an optical disk pickup.

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