JPH09289358A - Netride semiconductor laser device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-efficiency specified GaAlInN laser element having an optical guide structure having a refractive index distribution in horizontal direction by forming a ridge stripe-like second conductivity type upper clad layer extending toward a resonator. SOLUTION: A Gax Aly In1-x-y N (0<=x<=1, 0<=y<=1, x+y<=1) laser element has a ridge stripe shape. The surface protection of a ridge stripe-like p-type GaAlN upper clad layer 21b may have a double layer structure formed by leaving a SiO2 film used for the selective growth and laminating an Al2 O3 film 9 thereon. Thus it is possible to suppress the poor current injection, lower the oscillation threshold level and reduce the astigmatic difference of the GaN compd. semiconductor laser element having the ridge strip structure as well as to double the protective film of the upper clad layer 21b to thereby elevate the protection effect and improve the lift of the laser element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride based semiconductor laser device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A gallium nitride-based compound semiconductor is a wide-gap semiconductor and has a direct transition type band structure, so that it is expected to be applied to a light emitting device having an emission wavelength in blue to ultraviolet.

In these applications, GaInN is used as the active layer G
A double hetero-type light emitting diode using aAlN as a cladding layer has been put into practical use, and development has been actively conducted toward the practical use of a semiconductor laser device. Such a semiconductor laser device uses a sapphire or SiC substrate and is manufactured 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). A schematic view of a compound semiconductor laser device manufactured conventionally is shown in FIGS.

The compound semiconductor laser device shown in FIG. 10 has a buffer layer 10 for lattice matching on a substrate 101.
2. The lower clad layer 103, the active layer 104, and the upper clad layer 105 are sequentially formed. Incidentally, reference numeral 1 in the drawing
Reference numeral 06 is a current blocking layer, and 107 and 108 are metal electrodes.
The compound semiconductor laser device shown in FIG.
Current injection is performed by the metal electrode 108 in contact with the cladding layer 105 in the opening of 06. In the element having such a structure, the current injected near the opening of the current blocking layer 106 spreads horizontally in the upper cladding layer 105, and therefore the current injection width in the active layer 104 is the current blocking layer 10.
6 is wider than the width of the opening. Further, in this element structure, since a structure for confining light in the horizontal direction is not built in, the current blocking layer 106 is caused by the difference in gain generated in the portion into which the current is injected and the portion in which the current is not injected.
An optical waveguide is formed below the opening in such a manner that the light intensity is concentrated (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, and a substrate 151 are provided on a substrate 151.
Active layer 154, upper cladding layer 155, current blocking layer 15
6, the contact layer 157 is sequentially formed. Incidentally, reference numerals 158 and 159 in the figure denote metal electrodes. In the compound semiconductor laser device shown in FIG. 11, the current device layer 156 is placed in the semiconductor multilayer laminated structure, and the current injection width is limited by this opening. Even in this case, the current spreads horizontally in the cladding layer 155, but the thickness of the cladding layer 155 can be made thinner than in the case of FIG. 10, so that the spreading of the current can be made smaller. Further, in the semiconductor laser device structure of FIG. 11, since the current blocking layer 156 is made of a material that absorbs the light emitted from the active layer, the current blocking layer 156 is formed between the lower part of the opening and the lower part other than the opening. The structure has a refractive index difference in the horizontal direction, and an optical waveguide is formed (hereinafter referred to as an internal current constriction structure).

[0006]

However, the above-mentioned 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, the current spreading in the horizontal direction in the cladding layer 105 causes the current injection efficiency to the active layer to be poor and the oscillation threshold value to be high. Furthermore, since the optical waveguide having the horizontal refractive index distribution is not built in, the horizontal wavefront is largely bent, and the astigmatic difference is as large as several tens of μm or more, and good condensing characteristics cannot be obtained. However, there is a problem that it is unsuitable for a light source of a pickup for an optical disk.

On the other hand, in the case of the compound semiconductor laser device having the internal current constriction structure as shown in FIG. 11, the above-mentioned problem is solved. That is, since the current injection efficiency to the active layer 154 is good, the oscillation threshold value can be lowered, and the optical waveguide having the horizontal refractive index distribution is built in, the horizontal wavefront has a small bend and the astigmatic difference occurs. Smaller than a few μm,
It is suitable as a light source for pickups for optical discs because it has good light-collecting characteristics.
It is well known that GaInP-based infrared to red light emitting semiconductor lasers are generally widely used.

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

When a dry etching method is applied to a gallium nitride-based material, a practical etching rate of several thousand Å can be achieved, but the dry etching rate varies within the wafer surface. Is as large as ± 25%.
Therefore, in the nitride-based compound semiconductor laser device having the standard structure shown in FIG. 11 in which the film thickness of the upper clad layer 155 is 0.2 μm and the film thickness of the current blocking layer 156 is 1 μm, the current blocking layer 156 is striped. The contact layer 157 and the upper clad layer 15 when removed by etching
At the interface of No. 5, a portion where the current blocking layer 156 is not completely removed by etching or a portion where etching is too advanced and the upper cladding layer 155 is removed by etching are formed in the same plane. Therefore, in the gallium nitride-based compound semiconductor laser device having the structure of FIG. 11, current injection failure, deterioration of crystal quality of the active layer, and the like occur.

An object of the present invention is to solve the above problems and to provide a highly efficient gallium nitride compound semiconductor laser device having an optical waveguide structure having a refractive index distribution in the horizontal direction, and a gallium nitride compound semiconductor laser having a high production yield. It is to provide a method for manufacturing an element.

[0011]

In a nitride semiconductor laser device according to the present invention, a first conductivity type lower clad layer, an active layer and a second conductivity type upper clad layer are laminated in this order on a substrate. _{Ga x Al y In 1-xy} N (0 <x ≦ 1,0 ≦ y
<1, X + Y ≦ 1) In the nitride semiconductor laser device, the second conductivity type upper cladding layer has a ridge stripe shape extending in the cavity direction.

The nitride semiconductor laser device of the present invention is characterized in that the substrate is a first conductivity type semiconductor substrate.

Further, the nitride-based semiconductor laser device of the present invention is characterized in that the substrate is an insulating substrate.

Further, the nitride-based semiconductor laser device of the present invention is characterized by having a protective layer on the surface of the ridge stripe-shaped second conductivity type upper cladding layer.

Further, the nitride semiconductor laser device of the present invention is characterized in that the protective film comprises two layers of aluminum oxide and silicon oxide.

Further, the nitride semiconductor laser device of the present invention is characterized in that the active layer has a quantum well structure.

The nitride semiconductor laser device of the present invention is characterized in that a dry etching method is used to form the ridge stripe shape.

The nitride semiconductor laser device of the present invention is characterized in that a selective growth method is used to form the ridge stripe shape.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

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

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

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

2A to 2C are sectional views showing the steps of producing a semiconductor laser of gallium nitride-based compound semiconductor according to the present invention. First, from the n-type (0001) silicon (Si) surface as a substrate,
The damaged layer on the surface was removed by subjecting the 6H—SiC substrate 1 which was turned off 5 degrees in the 1120> direction to surface treatment and then oxidizing treatment. This 6H-SiC substrate is MOC
After being set in the reactor of the VD apparatus and the reactor was sufficiently replaced with hydrogen, the temperature was raised to 1500 ° C. and kept for 10 minutes while flowing hydrogen and ammonia.
The surface of the C substrate 1 is cleaned.

Next, the substrate temperature is lowered to 1050 ° C., and 1
Once stabilized at 050 ° C, trimethylaluminum (hereinafter,
It is written as TMA. ) Is flowed at a rate of 3 × 10 ⁻⁵ mol / min and ammonia at 5 liters / min for 5 minutes to grow an AlN buffer layer 2 having a thickness of about 0.1 μm. A cross-sectional view after the above steps are shown in FIG.

Next, trimethylgallium (hereinafter, TMG)
It is written. ) 3 × 10 ^-5 mol / min, ammonia 5 / min
A silane gas as a doping material of liter and Si is caused to flow at 0.3 cc / min for 15 minutes to grow the n-type GaN layer 3 for lattice matching.

Next, in addition to ammonia and TMG, TM
A of ⁶ × 10 ^-6 mol / min and silane gas of 0.3 cc / min
Then, the n-type GaAlN lower clad layer 4 having a thickness of about 1 μm is grown by a treatment for 25 minutes. The electron density of this layer is 2x1
0 ¹⁸ cm ^-3 .

Next, the supply of TMG, TMA and silane gas is stopped and the temperature is lowered to 800.degree. Temperature 800
After stabilizing at ℃, TMG and trimethylindium (hereinafter referred to as TMI) are flowed at ⁴ × 10 ^-4 mol / min, and
The GaInN active layer 5 having a thickness of 10 nm is grown by processing for a second.

Next, the supply of TMG and TMI is stopped and the temperature is raised again to 1050.degree. Temperature is 1050 ℃
Once stabilized, TMG, TMA, and Cp ₂ Mg (cyclopentadienylmagnesium) as a p-type doping material are caused to flow at 5 × 10 ⁻⁶ mol / min for 25 minutes, and then treated for 25 minutes to form a GaAlN upper clad layer 6 of about 1 μm Mg-doped. Grow.

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

On the Mg-doped GaN contact layer 7 of the semiconductor device manufactured as described above, a stripe-shaped S having a width of 1 μm is formed by an electron beam evaporation method and a photolithography process.
The iO ₂ film 8 is formed. A sectional view after the above steps are shown in FIG.

Next, with a reactive ion etching device,
Striped S with etching gas containing chlorine as the main component
Etching was performed on the Mg-doped GaN layer contact layer 7 and the Mg-doped GaAlN upper cladding layer 6 other than the portion where the iO ₂ film 8 was formed. In this etching process, the Mg-doped GaAlN upper clad layer 6 has a thickness of 0.
The etching time is adjusted so that etching is completed with 2 μm left. Here, the etching condition is DC
By setting the bias to 200 V and the RF power to 300 W, the Mg-doped GaN contact layer 7 and Mg
The etching rate for both the doped GaAlN upper cladding layer 6 is 3000 Å / min, and the etching is about 4 minutes 20.
Seconds went. Under the above conditions, DC bias is ± 50V, R
The F power was ± 50 W, and the variation in etching rate was about ± 10%.

Next, heat treatment is performed at about 700 ° C. for about 20 minutes in a nitrogen atmosphere to reduce the resistance of the Mg-doped GaAlN upper cladding layer 6 and the GaN contact layer 7 and to make them p-type. By this treatment, the hole concentration of both layers is about 1 × 10 ¹⁸ c
m ^-3 . A cross-sectional view after the above process is completed is shown in FIG.
Shown in

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 stripe-shaped SiO ₂ film 8 having a width of 1 μm is removed by hydrofluoric acid. After washing with water and drying, the p-side electrode 10 of the Au / Ni laminated film is entirely formed on the upper surface of the ridge type stripe by the vacuum evaporation method.

Next, the mirror surface of the laser resonator is formed. An SiO ₂ film having a width of 500 μm is formed as a mask in a direction orthogonal to the electrode stripe formed by the Au / Ni laminated film 10
Electron beam evaporation is performed at intervals of 0 μm.

Next, Si having a stripe of 50 μm
The wafer on which the O ₂ film is formed is introduced into a reactive ion etching apparatus, and the gallium nitride-based semiconductor layer at 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 an etching method. Further, the 6H-SiC substrate 1 is polished and processed to have a thickness of about 100 μm, and the SiO ₂ film used as a mask is removed.

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

Finally, the laser element is completed by dividing it into chips by scribing and mounting them in a package by a usual method.

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

In the element manufactured by the dry etching manufacturing method shown in the first embodiment, typically 50 mA.
Laser oscillation was observed at a current of 10 and the emission angle characteristic was an ellipticity of 2 with a divergence angle of 24 ° in the vertical direction and a divergence angle of 12 ° in the horizontal direction, but the oscillation threshold was 3
0 to 100 mA, horizontal divergence angle of 10 to 2
It was within the range of 3 °. The astigmatic difference was 1 to 5 μm.

In this embodiment, an example of a blue light emitting semiconductor laser device using a GaInN layer as an active layer and GaAlN as a clad layer is shown, but the present invention is not limited to this combination, and a GaInN active layer / GaN clad layer may be used. Or a GaN active layer / GaAlN clad layer, or a combination of GaAlInN-based quaternary compounds as long as laser oscillation is possible.

(Second Embodiment) FIG. 3 shows a blue light emitting compound semiconductor laser device manufactured by a selective growth method for forming a ridge stripe shape. The same members as those in FIG. 1 are designated by the same reference numerals. Reference numeral 21a is p-type GaAlN
The upper clad layer, 21b is p-type GaAl grown selectively
The N upper cladding layer and 23 are SiO ₂ protective films. This compound semiconductor laser device is characterized in that it has a ridge stripe shape, and that the protective film is composed of two layers of silicon oxide and aluminum oxide on the surface of the p-type GaAlN upper cladding layer having the ridge stripe shape.

Next, a method of manufacturing the compound semiconductor laser device of the second embodiment will be described.

First, the fabrication is performed by the same method as in FIG. 2A of the first embodiment. This step is shown in FIG.

Next, as in the first embodiment, the n-type GaN layer 3, the n-type GaAlN lower clad layer 4, and the GaInN active layer 5 are laminated, the temperature is set to 1050 ° C., and 5 liters of ammonia per minute and TMG are added. A flow rate of 3 × 10 ⁻⁵ mol / min, TMA of ⁶ × 10 ⁻⁶ mol / min and Cp ₂ Mg of 5 × 10 ⁻⁶ mol / min are flown for 5 minutes to grow a 0.2 μm Mg-doped GaAlN upper cladding layer 21 a. The above steps are shown in FIG.

Next, on the surface of the Mg-doped GaAlN upper cladding layer 21a, S having an opening 22 having a width of 1 μm was formed by the electron beam evaporation method and the photolithography method.
An iO ₂ film 23 is formed. The above steps are shown in FIG.

After this, S having an opening 22 with a width of 1 μm
A wafer on which a double hetero structure made of a gallium nitride-based compound semiconductor is stacked, on which the io ₂ film 23 is formed, is MO.
After introducing into the CVD apparatus and thoroughly replacing the reactor of the MOCVD apparatus with hydrogen, the temperature was raised to 1050 ° C. while flowing hydrogen and ammonia, and when the temperature became stable at 1050 ° C., TMG was added at 3 × 10 ⁻⁵ mol / min, and TMA was added. ⁶ × 10 ⁻⁶ mol / min, Cp ₂ Mg 5 × 10 ⁻⁶ mol / min, ammonia 5 liter / min, and treated for 20 minutes to form 0.8 μm Mg in the opening 22 having a width of 1 μm.
The doped GaAlN upper cladding layer 21b is grown. 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 TMA alone is stopped and the GaN contact layer 7 doped with Mg of 0.5 μm is grown by growth for 10 minutes. As described above, a portion other than the SiO ₂ film 23 is selectively grown to form a ridge stripe shape which becomes an optical waveguide. A cross-sectional view after the above steps are shown in FIG.

Next, heat treatment is performed at about 700 ° C. for about 20 minutes in a nitrogen atmosphere to reduce the resistance of the Mg-doped GaAlN upper cladding layers 21a and 21b and the GaN contact layer 7 and to make them p-type. With this treatment, the hole concentration of both layers is about 1
It became x10 ¹⁸ cm ^-3 .

Then, using a normal photolithography method, Al is formed as a protective film on the surface other than the upper surface of the ridge stripe shape.
_{A 2} O ₃ film 9 is formed by an electron beam evaporation method, and the p-side electrode 1 of the Au / Ni laminated film is formed only on the upper surface of the ridge stripe shape.
0 is entirely formed by a vacuum evaporation method. A cross-sectional view after the above steps are shown in FIG. The SiO ₂ film used for the selective growth is left and the Al ₂ O ₃ film 9 is formed thereon.
By laminating, the surface protection of the p-type GaAlN upper cladding layer can be simplified to a two-layer structure.

Next, the mirror surface of the laser resonator is formed. An SiO ₂ film having a width of 500 μm is formed as a mask in a direction orthogonal to the electrode stripe formed by the Au / Ni laminated film 10
Electron beam evaporation is performed at intervals of 0 μm.

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

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

When a current is applied to the compound semiconductor laser device manufactured by using the above selective growth method, typically,
Laser oscillation at a blue wavelength of 432 nm was observed at a threshold current of 40 mA, and as an emission angle characteristic, an ellipticity of 2 was obtained with a vertical divergence angle of 24 ° and a horizontal divergence angle of 12 °. It was The astigmatic difference was 1 to 5 μm.

In the element manufactured in this embodiment, the oscillation threshold value is 38 mA to 42 mA, and the horizontal spread angle is 1.
The variation was in the range of 1.5 ° to 12.5 °, and it was shown that the control of the cladding layer thickness outside the ridge stripe was superior to the characteristics of the first embodiment. The film thickness controllability of the GaAlN cladding layer by the MOCVD method was about ± 2% in the φ2 inch substrate surface.

Further, in the compound semiconductor laser device shown in the second embodiment, the protective film of the upper clad layer on the outer side of the ridge stripe shape has two layers of aluminum oxide and silicon oxide, so that the protective effect is high. The device life is improved.

It should be noted that in this embodiment, as the substrate, 5 is formed in the <1120> direction from the n-type (0001) silicon (Si) surface.
Although an example using the 6H-SiC substrate 1 that has been turned off has been described, it can be realized by using a p-type SiC substrate. In this case, it is necessary to reverse the conductivity type of each semiconductor layer described in the embodiment. is there. Further, the same effect was obtained by using a substrate which was not turned off. In addition to 6H-SiC, 4
Even if an H-SiC substrate or a 2H-SiC substrate is used, the same or higher effect can be obtained.

Further, the ridge stripe shape does not have to be formed from the upper clad layer, and substantially the same effect can be obtained even if only the contact layer has the ridge stripe shape.

(Embodiment 3) In FIG. 6, as in (Embodiment 2), a blue light emitting compound semiconductor manufactured on an insulating substrate by using a selective growth method to form a ridge stripe shape. A laser element is shown. The same members as those in FIGS. 1 and 3 are designated by the same reference numerals. Reference numeral 55 is a single quantum well structure G
aInN active layer, 101 is an insulating substrate, and 102 is GaN
It is a buffer layer. This compound semiconductor laser device is characterized in that it has a ridge stripe shape, and that the protective film is composed of two layers of silicon oxide and aluminum oxide on the surface of the p-type GaAlN upper clad layer having the ridge stripe shape. This is the same as the second embodiment.

Next, a method of manufacturing the compound semiconductor laser device of the third embodiment will be described.

First, the fabrication is performed by the same method as in FIG. 4A of the third embodiment. This step is shown in FIG.

Next, as in the third embodiment, the n-type GaN layer 3, the n-type GaAlN lower cladding layer 4, and the single quantum well structure GaInN active layer 55 (20 Å) are stacked at a temperature of 1
050 ° C. To 5 liters per minute of ammonia per minute to TMG 3x10 ^-5 mol, TMA per minute 6x10 ^-6 mol and Cp ₂ Mg were run per minute 5x10 ^-6 mol, 0.43 .mu.m by treatment for 11 minutes Of the Mg-doped GaAlN upper cladding layer 21a is grown. A cross-sectional view after the above steps are shown in FIG.

Next, on the surface of the Mg-doped GaAlN upper cladding layer 21a, S having an opening 22 having a width of 1 μm was formed by the electron beam evaporation method and the photolithography method.
An iO ₂ film 23 is formed. A cross-sectional view after the above steps are shown in FIG.

After this, S having an opening 22 with a width of 1 μm
iO_TwoGallium nitride compound semiconductor with the film 23 formed
MO wafers with stacked double heterostructures
After using a CVD apparatus and thoroughly replacing the reactor with hydrogen,
The temperature was raised to 1050 ° C while flowing hydrogen and ammonia.
, And when the temperature stabilizes at 1050 ℃,
Minute 3x10^-FiveMoles, TMA 6 x 10 per minute^-6Mole, Cp
_Two 5 x 10 per minute of Mg ^-6Mol and ammonia 5 liters per minute
A 1 μm wide film is opened by treating with a torrent for 20 minutes.
About 0.8 μm of Mg-doped GaAlN in the mouth 22
The upper clad layer 21b is grown. This growth is an opening
Since it is selectively performed only in the opening 22,
SiO_Two No semiconductor layer grows on the film 23.

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

Next, heat treatment is performed at about 700 ° C. for about 20 minutes in a nitrogen atmosphere to reduce the resistance of the Mg-doped GaAlN upper cladding layers 21a and 21b and the GaN contact layer 7 and to make them p-type. With this treatment, the hole concentration of both layers is about 1
It became x10 ¹⁸ cm ^-3 .

Next, using conventional photolithography, the wafer whole surface of Al ₂ O ₃ film 9 is formed by an electron beam evaporation method as a protective layer, a ridge stripe Al places other than the shape ₂ O ₃ film 9, And the SiO ₂ film 23 are removed in stripes to form openings 222. A cross-sectional view after the above steps are shown in FIG.

Next, the wafer in which the opening 222 is formed is introduced into a reactive ion etching apparatus, and gallium nitride at the opening of the Al ₂ O ₃ film 9 and the SiO ₂ film 23 for forming the n-side electrode. The system semiconductor layer up to the n-type GaN layer 3 is removed by etching by a normal reactive ion beam etching method. A cross-sectional view after the above steps are shown in FIG.

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 entirely formed by the vacuum evaporation method only on the upper surface of the ridge stripe shape by using the ordinary photolithography method.

Next, the mirror surface of the laser resonator is formed. An SiO ₂ film having a width of 500 μm is formed as a mask in a direction orthogonal to the electrode stripe formed by the Au / Ni laminated film 10
Electron beam evaporation is performed at intervals of 0 μm.

Next, Si having a 50 μm stripe is used.
The wafer on which the O ₂ film is formed is introduced into a reactive ion etching apparatus, and the gallium nitride-based semiconductor layer at 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 an etching method. Further, the insulating substrate 101 is polished and processed to have a thickness of about 100 μm, and the SiO ₂ film used as a mask is removed.

Finally, the laser element is completed by dividing it into chips by scribing and mounting them in a package by a usual method.

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

In the element manufactured in this embodiment, the oscillation threshold value is 28 mA to 32 mA, and the horizontal spread angle is in the range of 9.5 ° to 10.5 °. It was shown that the controllability of the characteristics was further excellent as compared with.

Also, in the compound semiconductor laser device shown in the third embodiment, since the protective film of the upper clad layer outside the ridge stripe has two layers of aluminum oxide and silicon oxide, the protective effect is high. The device life is improved.

In the present embodiment, the device having the active layer having the single quantum well structure has been described, but the quantum well has a multiple quantum well structure in which a plurality of quantum wells exist, for example, a well layer having a thickness of 2
Three 0 Å InGaN layers as a barrier layer and a thickness of 30 Å
An element structure having a structure in which two GaN layers are alternately laminated may be used. In the case of multiple quantum well structure,
Considering good injection of carriers into each quantum well layer and reduction of driving voltage, the number of quantum wells is preferably 3 or less.

(Embodiment 4) In FIG. 9, as in (Embodiment 1), dry etching is used to form a ridge stripe shape, and a single quantum well structure GaInN formed on a conductive substrate. 1 illustrates a blue-emitting compound semiconductor laser device including an active layer. The same members as those in FIGS. 1, 3 and 6 are designated by the same reference numerals.

The method of manufacturing the compound semiconductor laser device of the fourth embodiment is the same as that of the first embodiment, except that the single quantum well structure GaInN active layer 55 is laminated. The manufacturing method is different.

Next, with a reactive ion etching device,
Striped S with etching gas containing chlorine as the main component
The Mg-doped GaN layer contact layer 7 and the Mg-doped GaAlN upper clad layer 6 other than the portion where the iO ₂ film 8 is formed are etched in the same manner. However, in this etching step, the Mg-doped GaAlN upper clad layer 6 is This is different from the case of the first embodiment in that the etching time is adjusted so that the etching is completed while leaving 0.43 μm. Here, by setting the DC bias to 200 V and the RF power to 300 W as etching conditions, the GaN contact layer 7 and the Mg-doped GaA are formed.
Both the 1N upper clad layer 6 have an etching rate of 3000Å
/ Min, and etching was performed for about 3 minutes and 25 seconds. Under the above conditions, DC bias is ± 50 V, RF power is ± 50
W, and the variation in etching rate was about ± 10%.

Next, a heat treatment at about 700 ° C. in a nitrogen atmosphere was also performed as in the first embodiment.

Further, Au / on the upper surface of the ridge type stripe
The steps of forming the p-side electrode 10 of the Ni laminated film, 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 were performed in the same manner as in the first embodiment.

Finally, the laser element is completed by dividing it into chips by scribing and mounting them in a package by a usual method.

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 device using a GaInN layer as an active layer and GaAlN as a cladding layer is shown, but the invention is not limited to this combination, and a GaInN active layer / GaN cladding layer is also available. It is also the same as in the first embodiment that a combination of a GaAlInN-based quaternary compound may be used as long as it is a combination of GaN active layer / GaAlN clad layer or laser oscillation.

Further, in the present embodiment as well, as in the case of the third embodiment, an element having an active layer of a single quantum well structure has been described, but an element having a multiple quantum well structure having a plurality of quantum wells. The structure may be good, and in the case of a multiple quantum well structure, good injection of carriers into each quantum well layer,
Considering the reduction of the driving voltage, the number of quantum wells is preferably 3 or less, as in the case of the third embodiment.

[0085]

The gallium nitride-based compound semiconductor laser device having the ridge stripe structure as described in the present embodiment causes the current injection failure due to the variation of etching like the conventional compound semiconductor laser device. , The oscillation threshold was low, and the astigmatic difference was small.

The ridge stripe shape of the compound semiconductor laser according to the present invention can be formed by either the dry etching method or the selective growth method. In particular, when the selective growth method is used, the film thickness controllability of the upper clad layer outside the ridge stripe shape is excellent, and the variation of the element is improved. Further, by providing the protective layer on the side surface where the interface between the contact layer and the upper clad layer is present, the deterioration of the current injection path can be prevented. Furthermore, by forming the protective film of the upper clad layer into two layers, the semiconductor laser device The protective effect is high and the device life is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in the first embodiment.

FIG. 3 is a sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in the second embodiment.

FIG. 4 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.

FIG. 5 is a diagram showing the relationship between the thickness of the upper clad layer outside the ridge stripe shape and the horizontal radiation angle.

FIG. 6 is a cross-sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in a third embodiment.

FIG. 7 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.

FIG. 8 is a diagram showing a relationship between a horizontal radiation angle and an upper clad layer thickness outside a ridge stripe shape in a device having a single quantum well active layer structure.

FIG. 9 is a sectional view of a gallium nitride based semiconductor laser device having a ridge stripe shape shown in the fourth embodiment.

FIG. 10 is a sectional view of a semiconductor laser device having a conventional electrode stripe structure.

FIG. 11 is a sectional view of a conventional semiconductor laser device having an internal current constriction structure.

[Explanation of symbols]

1 6H-SiC substrate 101 Insulating substrate 2 AlN buffer layer 102 GaN buffer layer 3 n-type GaN layer 4 n-type GaAlN lower clad 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 21a p-type GaAlN upper clad layer 21b selectively grown p-type GaAlN upper clad layer 22 opening 222 opening 23 SiO ₂ membranes

Claims (8)

[Claims] 1. A on a substrate, a first conductivity type lower cladding layer, the active _{layer, Ga x Al y In 1-} xy N (0 <x ≦ 1 formed by laminating a second conductive type upper cladding layer in this order, 0 ≦ y <
1. A nitride-based semiconductor laser device, wherein in the compound semiconductor laser device of (1), (X + Y ≦ 1), the second conductivity type upper cladding layer has a ridge stripe shape extending in the cavity direction. 2. A nitride semiconductor laser device, wherein the substrate is a first conductivity type semiconductor substrate. 3. A nitride semiconductor laser device, wherein the substrate is an insulating substrate. 4. The nitride semiconductor laser device according to claim 1, wherein a protective layer is provided on the surface of the ridge stripe-shaped second conductivity type upper cladding layer. 5. The nitride semiconductor laser device according to claim 4, wherein the protective film comprises two layers of aluminum oxide and silicon oxide. 6. The nitride semiconductor laser device according to claim 1, wherein the active layer has a quantum well structure. 7. The method of manufacturing a nitride semiconductor laser device according to claim 1, wherein a dry etching method is used to form the ridge stripe shape. 8. The selective growth method is used to form the ridge stripe shape.
7. The nitride semiconductor laser device according to any one of 6 above.