JP2003179311A - GaN SEMICONDUCTOR LASER ELEMENT AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN semiconductor laser element whose threshold current value and operation voltage are lower than a conventional air-ridge type GaN semiconductor laser element. <P>SOLUTION: The GaN semiconductor laser element 60 has a laminated structure in which an n-AlGaN clad layer 64, an n-GaN guide layer 66, an InGaN quantum well active layer 68, a p-GaN guide layer 70, a p-AlGaN clad layer 72, and a p-GaN contact layer 74 are laminated on an n-type GaN substrate 62 having a ridge structure 61 in <1-100>±10° direction, with (11-20) surface as a main surface. An n-clad layer is composed of an upper surface part 64a having (0001) surface, a slope part 64b having a slope of (11-22) surface, and a flat part 64c extending along (11-20) surface from the lower end of the tilted part, with a ridge structure embedded. The n-guide layer, active layer, p-guide layer, and p-clad layer are formed into the same shape along the n-clad layer. A p-side electrode 78 is formed on the p-GaN contact layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN-based semiconductor laser device and a method for manufacturing the same, and more specifically, a semiconductor laser device having a low threshold current value and a low operating voltage, which is optimum as a light source for an optical pickup or the like. , And a manufacturing method thereof.

[0002]

Ga on a sapphire or GaN substrate.
A GaN-based semiconductor laser device having a laminated structure of N-based compound semiconductor layers has been attracting attention as a light-emitting device that emits light in a short wavelength range from an ultraviolet region to a green region. For example, a contact layer and an upper clad layer are air-ridge type. A semiconductor laser device having a current constriction structure processed into the above has been developed and commercialized.

Various air ridge type GaN-based semiconductor laser devices have been proposed in the past.
JP-A-00-91696 discloses an air-ridge type GaN-based semiconductor laser device as described below.
Here, referring to FIG. 4, a conventional air ridge type GaN is used.
JP-A-2000-2000 as a typical example of a semiconductor laser device
The structure of the GaN-based semiconductor laser device disclosed in Japanese Patent Publication No. 91696 will be described. FIG. 4 is a sectional view showing the structure of a conventional air-ridge type GaN-based semiconductor laser device.
As shown in FIG. 4, the conventional GaN-based semiconductor laser device 16 has an AlGaN buffer layer 2, a GaN layer 3, and an n-GaN on the c-plane {(1-100) plane} of the sapphire substrate 1.
Layer 4, n-InGaN crack prevention layer 5, n-first cladding layer 6, MQW light emitting layer 7, p-second cladding layer 8, p
-A low temperature GaN growth layer 9, a p-third clad layer 10, and a p-GaN contact layer 11 are laminated.

Of the laminated structure, the p-low temperature GaN growth layer 9,
The p-third cladding layer 10 and the p-GaN contact layer 11 are formed as a stripe ridge structure, and the p-side electrode 12 is formed on the p-GaN contact layer 11.
However, the laminated structure from the upper layer of the n-GaN layer 4 to the p-second cladding layer 8 is formed as a mesa structure extending in the same direction as the ridge structure, and n is exposed on the exposed n-GaN layer 4. The side electrode 13 is formed. In order to perform current constriction and protect the exposed portion of the pn junction, both side surfaces of the ridge structure, the upper surface of the flat portion of the p-second cladding layer 8, except the p-side electrode 12 and the n-side electrode 13, The SiO ₂ film 14 is formed on the upper surface of the GaN layer 4 and the side surfaces from the p-second cladding layer 8 to the n-GaN layer 4.

[0005]

By the way, when a GaN-based semiconductor laser device is used as a light source of an optical pickup for writing / reading to / from an optical disk, a threshold current value is further increased than before in order to reduce power consumption. Low GaN
System semiconductor laser devices are required. The threshold current value I _th of the semiconductor laser device is given by the following equation. I _th = J _th × W × L where J _th is the threshold current density, W is the stripe width (active layer width) of the semiconductor laser element, and L is the stripe length (active layer length). As can be seen from this equation, in order to lower the threshold current value, it is necessary to reduce the stripe length and width, and the stripe width is an important parameter that determines the threshold current value. Even in the semiconductor laser device, the smaller the stripe width, the lower the threshold current value.

However, the conventional air ridge type Ga described above is used.
In the N-based semiconductor laser device, it was difficult to reduce the threshold current value by narrowing the stripe-shaped current injection region for the following reasons. First, it is extremely difficult to control the stripe-shaped current injection region, that is, the ridge width to 2 μm or less, due to the limitation of the lithography process when the laminated structure is etched by the RIE method or the like to form the stripe-shaped ridge structure. Because it is. Furthermore, the narrower the ridge width, the smaller the contact area between the p-contact layer and the p-side electrode and the larger the contact resistance, which causes a problem that the operating voltage increases.

Second, there is a problem of etching accuracy when the ridge structure is formed by etching the laminated structure by the RIE method or the like. In order to reduce the threshold current value as much as possible and increase the lateral refractive index difference to enhance the stability of the transverse mode, for example, 0.15 μm above the active layer.
It is necessary to etch to about m. But,
Actually, since each growth film constituting the laminated structure has a film thickness distribution and the etching rate at the time of etching by the RIE method or the like also varies, it is difficult to form a ridge structure by etching with good controllability. It is very difficult to do over-etching and damage the active layer,
On the contrary, this is because the laser characteristics vary due to etching residue.

Therefore, another current constriction structure is disclosed in Japanese Patent Laid-Open No.
No. 0-58981. Here, FIG.
The configuration of the GaN-based semiconductor laser device disclosed in Japanese Patent Laid-Open No. 2000-58981 will be described with reference to FIG.
As shown in FIG. 5, the conventional GaN-based semiconductor laser device 20 has an n-type on the (11-20) plane of a sapphire substrate 22.
-Type GaN contact layer 24, n-type AlGaN cladding layer 26, n-type optical guide layer 28, width 1 in the <1-100> direction
2000 Å Thickness with stripe-shaped opening 30 of μm
SiO ₂ mask 32, an n-type GaN light guide layer 34 formed in the opening 30, an InGaN-based quantum well structure active layer 36, a p-type GaN light guide layer 38, and a p-type AlGaN
The layered structure includes a clad layer 40 and a p-type GaN contact layer 42.

In the present GaN-based semiconductor laser device 20, the p-type optical guide layer 38, the p-type AlGaN cladding layer 40, and the p-type GaN contact layer 42 of the laminated structure are striped ridges on the stepped active layer 36. Is formed as a part. In addition, the SiO ₂ mask 32, the n-type light guide layer 28, the n-type AlGaN cladding layer 26, and the n-type GaN
The laminated structure up to the upper layer of the contact layer 24 is formed as a mesa structure extending in the same direction as the stripe ridge portion, and the n-side electrode 44 is formed on the exposed n-type GaN contact layer 24. Further, the p-side electrode 46 is formed on the entire surface of the stripe ridge portion and on the exposed SiO ₂ mask 32.
Are formed.

In the present GaN-based semiconductor laser device 20, the current confinement structure is formed by the SiO ₂ mask 32 other than the region of the opening 30. And the SiO ₂ mask 3
N-type GaN light guide layer 34, active layer 36, p-type GaN light guide layer 38, p-type A
The lGaN cladding layer 40 and the p-type GaN contact layer 42 are grown to form a ridge structure. However, when the InGaN layer is selectively grown in a stripe shape, Si flies from the SiO ₂ mask 32 and adversely affects the initial process of re-growth. For this reason, it is actually difficult to form an InGaN layer having a steep interface, and there is a problem that the luminous efficiency of the active layer is reduced, which is also difficult to put into practical use.

Therefore, an object of the present invention is to provide a GaN-based semiconductor laser device which has a lower threshold current value and a lower operating voltage than the conventional air-ridge type GaN-based semiconductor laser device and which is optimal as a light source for an optical pickup or the like. That is.

[0012]

Means for Solving the Problems In the course of research for solving the above problems, the present inventor has extended in the <1-100> direction, or a direction close thereto, for example, <1-100> ± 10 °, A stepped substrate 47 having a stripe-shaped ridge portion having a stripe width of 1 μm, a height of 0.5 μm, and a top portion having the same (0001) plane as the substrate main surface was prepared. As shown, Experiment 1 for forming the InGaN layer 48 was conducted.

As a result, as shown in FIG. 6, by optimizing the growth conditions such as the growth rate and the group V / group III molar ratio, I on the ridge portion, that is, on the (0001) plane
The nGaN layer 48a has the largest film thickness, the InGaN layer 48c on the main surface of the substrate next to the ridge part has the largest film thickness, grows along the side wall of the ridge part, and has a (11-22) plane growth surface. It has been found that the thickness of the InGaN layer 48b is the thinnest and the thickness can be extremely thin. That is, since the thickness of the InGaN layer 48b grown along the side wall of the ridge portion is extremely thin, the stripe-shaped InGaN layer 48a can be formed as an active layer substantially only on the ridge portion, and the ridge portion can be formed. It was also found that the stripe width of the upper InGaN layer 48a is closely related to the stripe width at the top of the ridge. In particular, In _0.07 Ga _0.93 N / In
_In the growth of the _0.02 Ga _0.98 N quantum well active layer, the growth rate on the (11-22) plane along the sidewall of the ridge is slow, and the growth is substantially performed only on the (0001) plane on the top of the ridge structure. It turns out that it is also possible. This is shown in Figure 7.
A clear copy of the TEM photograph shown in FIG. The original TEM photograph of FIG. 7 is submitted as a reference photograph together with the specification.

The present inventor also conducted an experiment 2 for forming an AlGaN layer on the stepped substrate 47 as shown in FIG. As a result, the AlGaN layer grown at the growth temperature of 800 ° C. to 1040 ° C. is the AlGaN layer 4 on the ridge portion.
9a has the lowest Al%, then the AlGaN layer 49c on the main surface of the substrate on the side of the ridge has the lowest Al%, grows along the side wall of the ridge, and has an (11-22) -faced growth surface. It was found that the Al% of 49b was the highest.
For example, when the p-type cladding layer is grown at 1003 ° C., the Al% of the AlGaN layer 49a on the ridge is 8.7.
%, AlGaN layer 4 having a (11-22) plane of growth
The Al% of 9b was 14.1%. The electrical resistance of the Mg-doped p-type AlGaN layer increases as the Al composition increases. Therefore, by growing the p-type cladding layer at 1003 ° C., the p-type cladding layer was grown along the sidewall of the ridge (1
It was found that the electric resistance of the AlGaN layer 49b having the 1-22) plane was higher than that of the AlGaN layer 49a on the ridge. Conversely, the growth temperature 105
At 3 ° C., the Al% of the AlGaN layer 49a on the ridge portion is 13.6%, and the AlG having a (11-22) plane growth surface.
The Al% of the aN layer 49b was 5.0%.

From the above experiment, 800 ° C. or more and 1040 ° C.
By forming an AlGaN layer on the stepped substrate at the following growth temperature and controlling the Al composition, a current injection region having a low electric resistance on the ridge portion and a current constriction region other than the ridge portion are formed separately. It turns out that I can do it.

In order to achieve the above object, the GaN-based semiconductor laser device according to the present invention is based on the above findings.
A substrate having a striped ridge portion having a top portion in the same plane direction as the main surface of the substrate on the main surface of the substrate, and a film epitaxially grown on the ridge portion of the substrate and formed a film on the top of the ridge portion. Same as the main surface, which is formed on the upper surface with the growth surface in the azimuth direction, on the sidewall of the ridge portion, on the side surface of the ridge portion, and on the main surface of the substrate on the side of the ridge portion. A first G having a flat portion having a plane orientation as a growth surface
An aN-based compound semiconductor layer and a stacked structure of a GaN-based compound semiconductor layer including an active layer, which is stacked on the first compound semiconductor layer along the first compound semiconductor layer in substantially the same shape. It is characterized by that.

In the present invention, the GaN compound semiconductor means a group III nitride compound semiconductor containing at least Ga and N, and is, for example, GaN, AlGaN, InGaN, AlG.
aInN and AlBGaInN. In the present invention, the cross-sectional shape of the ridge portion is preferably trapezoidal or rectangular, although there is no limitation as long as the top surface of the top portion has the same plane orientation as the main surface of the substrate. The ridge structure usually has a width of 5 μm or less and a height of 0.1 μm or more. The striped ridge portion may be formed on the main surface of the substrate, or may be formed on the GaN-based compound semiconductor layer formed on the main surface of the substrate. Further, the method of forming the ridge portion is not limited, and for example, the substrate or the GaN-based compound semiconductor layer on the substrate may be etched to form the ridge portion, or the GaN-based compound semiconductor layer may be formed on the substrate in a ridge shape. Alternatively, the ridge portion may be formed by selective growth.

In a preferred embodiment of the present invention, the main surface is (0
001) plane, and the extension direction of the ridge is <1-100
Within the range of> ± 10 °, the growth surface of the inclined surface portion is (11-
22) surface. The active layer has an upper surface portion that functions as a light emitting region, and an inclined surface portion that is thinner than the upper surface portion and has a low light emitting property and that does not substantially contribute to light emission.
The upper cladding layer is formed as an aN-based quantum well structure layer, and the upper clad layer has an upper surface portion having a low electric resistance and functioning as a current injection region, and an inclined surface portion having a higher electric resistance than the upper surface portion and functioning as a current confinement region. A GaN contact layer formed of a semiconductor layer and below the upper electrode,
It is laminated on the upper clad layer in the same shape as the upper electrode.

In a preferred embodiment of the present invention, the width of the upper surface of the active layer can be made narrow, for example, 1 μm or less,
The threshold current value can be made smaller than that of the conventional GaN-based semiconductor laser device. Further, since the contact area between the upper electrode and the GaN contact layer can be increased, the operating voltage can be lowered as compared with the conventional GaN-based semiconductor laser device.

According to the epitaxial growth method on a stepped substrate according to the present invention, G is formed on a stepped substrate having a striped ridge portion having a top portion in the same plane orientation as the main surface of the substrate on the main surface of the substrate.
A method for epitaxially growing an aN-based compound semiconductor layer, which is formed on a top portion of a ridge portion, a top surface portion having a growth plane in the same plane orientation as the main surface, and a side wall of the ridge portion. The ridge portion of the substrate is a GaN-based compound semiconductor layer having an inclined surface portion having a growth surface with a plane orientation and a flat portion formed on the main surface of the substrate next to the ridge portion and having a growth surface in the same plane orientation as the main surface. In the step of epitaxially growing the GaN-based compound semiconductor layer, at least the growth temperature and V / II of the source gas are included.
By adjusting the growth conditions including the I ratio to control the growth rate ratio of the upper surface portion and the inclined surface portion, and by adjusting the ridge width and the ridge height of the ridge portion, the upper surface portion and the upper surface of the desired film thickness and width can be obtained. It is characterized in that a GaN-based compound semiconductor layer having an inclined surface portion having a smaller film thickness than that of the above portion is formed.

In the method of the present invention, the type of epitaxial growth method is not limited, and for example, the MOCVD method can be preferably adopted. A method for producing a GaN-based semiconductor laser device by applying the method of the present invention has a top portion having the same plane orientation as the main surface of the (0001) plane of the substrate and extends in an orientation of <1-100> ± 10 °. A method for producing a GaN-based semiconductor laser device on a stepped substrate having an existing striped ridge portion, wherein the growth temperature is 800 ° C. or higher and 1040 ° C. or lower according to the epitaxial growth method on the stepped substrate according to claim 4. An upper surface portion having a (0001) plane and a (1
An active layer having an InGaN-based quantum well structure and an upper clad layer composed of an AlGaN-based compound semiconductor layer, the active layer having an upper surface portion functioning as a light emitting region; The upper clad layer has an inclined surface portion that is thinner than the upper surface portion, has a low light emitting property, and does not substantially contribute to light emission. The upper clad layer has an upper surface portion that has a low electric resistance and functions as a current injection region. It is characterized by having an inclined surface portion which is higher than the portion and functions as a current confinement region. By the method of the present invention, a GaN-based semiconductor laser device having a ridge structure with a stripe width of 1 μm or less can be manufactured.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings by way of example embodiments. The film forming method, the composition and film thickness of the compound semiconductor layer, the ridge width, the process conditions and the like shown in the following embodiments are merely examples for facilitating the understanding of the present invention. It is not limited to this example. Embodiment Example 1 of Semiconductor Laser Device This embodiment example is an example in which the GaN-based semiconductor laser device according to the present invention is applied to a GaN-based semiconductor laser device formed on a GaN substrate, and FIG. FIG. 3 is a schematic cross-sectional view showing the configuration of the GaN-based semiconductor laser device of FIG. As shown in FIG. 1, the GaN-based semiconductor laser device 60 of the present embodiment has a (1000) plane as a main surface and <1-100.
> Direction or close thereto, for example <1-100> ± 10
The n-Al _0.08 Ga _0.92 N cladding layer 64, n- formed in order on the n-type GaN substrate 62 provided with the ridge portion 61 having a stripe width of 1 μm and a height of 1.5 μm in the direction of °.
GaN guide layer 66, In _0.07 Ga _0.93 N / In _0.02 G
a _0.98 N quantum well active layer 68, p-GaN guide layer 7
0, p-Al _{0.08 with} carrier concentration of about 1 × 10 ¹⁷ cm ^-3
Ga _0.92 N cladding layer 72, and carrier concentration is about 1 ×
It has a laminated structure of 10 ⁻¹⁸ cm ⁻³ p-GaN contact layer 74. The ridge portion 61 has a top portion having a (0001) plane with the same plane orientation as the main surface of the substrate 62.

The n-AlGaN cladding layer 64 has an upper surface portion 64a having a (0001) plane on the ridge portion and a (11)
It is composed of an inclined surface portion 64b having an inclined surface of −22) surface and a flat portion 64c extending from the lower end of the inclined portion 64b along the (0001) surface and burying the ridge portion 61 of the n-type GaN substrate 62. There is. n-GaN guide layer 6
6, active layer 68, p-GaN guide layer 70, and p-A
The lGaN clad layer 72 is formed in the same shape along the n-AlGaN clad layer 64.

The p-GaN contact layer 74 is made of p-Al.
It is formed only on the upper surface portion 72a of the GaN clad layer 72, and a protective film 76 made of a SiO ₂ film is further formed on the p-AlGaN clad layer 72 except for the region of the p-GaN contact layer 74. . In addition, Ni / Pt /
A p-side electrode 78 such as an Au metal film is formed on the p-GaN contact layer 74. That is, the p-GaN contact layer 74 under the p-side electrode 78 is laminated on the p-AlGaN cladding layer 72 in the same shape as the p-side electrode 78. Further, an n-side electrode 79 is formed in the central region of the back surface of the GaN substrate 62, and protective films 76 are formed on both sides of the n-side electrode 79.
Is deposited.

In the GaN-based semiconductor laser device 60, the width and height of the ridge portion 61 are set to appropriate values, and n-A
(0 of the lGaN clad layer 64 and the quantum well active layer 68
The stripe width of the active layer on the ridge portion 61 is controlled by adjusting the growth rate ratio of the (001) plane and the (11-22) plane to the growth temperature and the V / III ratio of the source gas. You can In the present embodiment example, the active layer 68
Has a stripe width of 0.5 μm. In addition, p-Al
In the GaN clad layer 72, since the electric resistance of the inclined surface portion 72b is higher than that of the upper surface portion 72a, the injection current is p−.
It is difficult to leak to the inclined surface portion 72b of the AlGaN cladding layer 72. Therefore, the light output-injection current characteristic is good. Furthermore, since the areas of the p-side electrode 78 and the p-GaN contact layer 74 can be increased, the operating voltage can be reduced.

Embodiment 2 of Semiconductor Laser Device This embodiment is an example in which the GaN-based semiconductor laser device according to the present invention is applied to a GaN-based semiconductor laser device formed on a sapphire substrate, and FIG. Ga of the embodiment example
It is a typical sectional view showing the composition of the N type semiconductor laser device. The GaN-based semiconductor laser device 80 of the present embodiment example is
As shown in FIG. 2, the substrate is a sapphire substrate 82, and the n-GaN contact layer 8 is formed on the sapphire substrate 82.
4 is provided, the main surface is the (0001) plane,
<1-100> direction or close thereto, for example, <1-1
Stripe width 1 μm extending in the direction of 00> ± 10 °,
A ridge portion 83 having a height of 1.5 μm is provided in the n-GaN contact layer 84, and a stacked structure above the upper layer portion of the n-GaN contact layer 84 extends in the same direction as the ridge portion. The semiconductor laser device 6 according to the first embodiment except that the n-side electrode 86 is formed and the n-side electrode 86 is provided on the n-GaN contact layer 84.
The GaN-based semiconductor laser device 60 has the same structure as that of the GaN semiconductor laser device 60 according to the first embodiment and can achieve the same effect as that of the GaN-based semiconductor laser device 60 of the first embodiment.

Although the sapphire substrate 82 is used in this embodiment, a SiC substrate may be used. Also,
A laminated structure may be formed on the sapphire substrate 82 or the SiC substrate via a low temperature buffer layer. Further, when the GaN layer is epitaxially grown on these substrates, it is also possible to form the defect reduction region by utilizing lateral growth and form the laminated structure on it.

Example of Embodiment of Method for Manufacturing Semiconductor Laser Device This embodiment is an example of an embodiment in which the method for manufacturing a semiconductor laser device according to the present invention is applied to the GaN-based semiconductor laser device 60 described above. 3 (a) to 3 (c) are cross-sectional views of respective steps when manufacturing a semiconductor laser device according to the present embodiment example. First, as shown in FIG. 3A, the (0001) plane of the n-type GaN substrate 62 is RI.
Etching is performed by the E method to form a ridge portion 61 having a ridge width W of 1 μm and a height H of 1.5 μm in a <1-100> direction or a direction close thereto, for example, a <1-100> ± 10 ° direction. Form.

Then, as shown in FIG. 3B, the ridge portion 61 is grown by MOCVD at a growth temperature of 1000 ° C.
The n-Al _0.08 Ga _0.92 N cladding layer 64 is epitaxially grown. As a result, (000
1) a top surface portion 64a having a surface, an inclined surface portion 64b having a (11-22) surface growth surface, and a flat portion 64c extending from the lower end of the inclined portion 64b along the (0001) surface of the n-type GaN substrate 62. The n-AlGaN clad layer 64 is formed by filling the ridge portion of the n-type GaN substrate 62.

Then, on the n-AlGaN cladding layer 64, an n-type is formed by MOCVD at a growth temperature of 1000.degree.
GaN guide layer 66, In _0.07 Ga _0.93 N / In _0.02 G
a _{0. 98} N quantum well active layer 68, p-GaN guide layer 7
0, p-Al _0.08 Ga _0.92 N cladding layer 72 and p-G
The aN contact layer 74 is sequentially epitaxially grown to form a laminated structure as shown in FIG.

In the method of this embodiment, when forming a laminated structure, the growth rate ratio of the (0001) plane and the (11-22) plane of each layer is determined by the growth temperature, the V / III ratio of the source gas, and the like. By adjusting the conditions and setting the width and height of the ridge portion 61 to appropriate values, the thickness and width of each layer on the ridge portion 61 can be controlled. In the present embodiment, the growth temperature is 1000 ° C., and the V / III ratio of the source gas when the n-AlGaN cladding layer 64 and the p-AlGaN cladding layer 72 are formed is 10,000.

As a result, the p-AlGaN cladding layer 7 is formed.
The Al compositions of the (0001) plane and the (11-22) plane of No. 2 are 8.7% and 14.1%, respectively, and the upper surface portion having the (0001) plane naturally becomes the current injection region. , The inclined surface portion having the (11-22) plane as a growth surface serves as a current constriction region. In addition, the quantum well active layer 68 is (11-
22) surface has a slow growth rate and hardly grows,
Since the growth rate is high on the (0001) plane, it can be grown only on the (0001) plane on the ridge portion 61. Therefore, as the width of the active layer, for example, a narrow waveguide structure having a width smaller than 1 μm can be formed.

Next, a p-side electrode 78 made of a Ni / Pt / Au metal multilayer film or the like is selectively formed on the p-GaN contact layer 74, and then the ridge portion 61 is formed by the RIE method using the p-side electrode 78 as a mask. The p-GaN contact layer 74 other than the upper region is etched to have a width of 0.1 μm, for example.
The p-GaN contact layer 74 is formed as described above, and the inclined surface portion and the flat portion of the p-AlGaN cladding layer 72 are exposed as shown in FIG. Next, although not shown, GaN
An n-side electrode 79 is provided on the back surface of the substrate 62, and a protective film 76 is further provided.
To form a film.

In this embodiment, the method of manufacturing the GaN-based semiconductor laser device 60 on the n-type GaN substrate 62 has been described as an example, but the GaN-based semiconductor laser device 80 on the sapphire substrate 82 (see FIG. 2). The same can be applied to the case of manufacturing. However, in that case, the sapphire substrate 8
It is preferable to form a base layer of the n-GaN contact layer 84 by providing a low-temperature growth layer of GaN or applying a lateral growth method on the second layer.

[0035]

According to the present invention, the substrate is epitaxially grown on the ridge portion of the substrate and has an upper surface portion on the ridge portion, an inclined surface portion grown along the side wall of the ridge portion, and a flat portion beside the ridge portion. A first GaN-based compound semiconductor layer and a laminated structure of a GaN-based compound semiconductor layer that is laminated on the first compound semiconductor layer along the first compound semiconductor layer in substantially the same shape and includes an active layer. By forming a semiconductor laser device having a G having an extremely narrow waveguide structure,
It is possible to realize an aN semiconductor laser device and reduce the threshold current value. Also, G under the upper electrode
By stacking the aN contact layer on the upper clad layer in the same shape as the upper electrode, a GaN-based semiconductor laser device having a large electrode area and a low operating voltage can be realized. Further, the method of the present invention realizes a method for suitably manufacturing the GaN-based semiconductor laser device of the present invention, and RI
Since the step of etching the compound semiconductor layer to just above the active layer by the E method or the like to form the ridge portion is not required, the laser characteristics do not vary and the yield is improved. By applying the method of the present invention, it is possible to achieve lower power consumption, higher reliability, and higher yield of the GaN-based semiconductor laser device.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the configuration of a GaN-based semiconductor laser device according to a first embodiment.

FIG. 2 is a schematic cross-sectional view showing the configuration of a GaN-based semiconductor laser device according to a second embodiment.

FIG. 3A to FIG. 3C are cross-sectional views for each step in manufacturing a semiconductor laser device according to the present embodiment example.

FIG. 4 is a sectional view showing a configuration of a conventional air ridge type GaN-based semiconductor laser device.

FIG. 5 is a cross-sectional view showing the structure of another conventional air ridge type GaN-based semiconductor laser device.

FIG. 6 is a schematic cross-sectional view of a GaN layer on a stepped substrate.

FIG. 7 is a copy of a TEM photograph.

FIG. 8 is a schematic cross-sectional view of an AlGaN layer on a stepped substrate.

[Explanation of symbols]

1 ... Sapphire substrate, 2 ... AlGaN buffer layer,
3 ... GaN layer, 4 ... n-GaN layer, 5 ... n-In
GaN crack prevention layer, 6 ... n-first cladding layer, 7
...... MQW light emitting layer, 8 ...... p-second cladding layer, 9 ......
p-low temperature GaN growth layer, 10 ... p-third cladding layer,
11 ... p-GaN contact layer, 12 ... p-side electrode,
13 ... N-side electrode, 14 ... SiO ₂ film, 16 ... Conventional GaN-based semiconductor laser device, 20 ... Another conventional Ga
N-based semiconductor laser device, 22 ... Sapphire substrate, 24
... n-type GaN contact layer, 26 ... n-type AlGaN
Cladding layer, 28 ... N-type light guide layer, 30 ... Stripe-shaped opening, 32 ... SiO ₂ mask, 34 ... N-type GaN light guide layer, 36 ... InGaN / InGaN quantum well structure active layer, 38 ... P-type GaN optical guide layer, 4
0 ... p-type AlGaN cladding layer, 42 ... p-type GaN
Contact layer, 44 ... n side electrode, 46 ... p side electrode,
60 ... GaN-based semiconductor laser device of Example 1, 6
1 ... ridge structure, 62 ... n-type GaN substrate, 64 ...
n-Al _0.08 Ga _0.92 N cladding layer, 64a ... upper surface portion, 64b ... inclined surface portion, 64c ... flat portion, 66 ...
n-GaN guide layer, 68 ... In _0.07 Ga _0.93 N / I
n _0.02 Ga _0.98 N quantum well active layer, 70 ... p-GaN
Guide layer, 72 ... p-Al _0.08 Ga _0.92 N cladding layer, 74 ... p-GaN contact layer, 76 ... Protective film, 78 ... P-side electrode, 79 ... N-side electrode, 80 ... Embodiment Example 2 GaN-based semiconductor laser device, 82 ... Sapphire substrate, 83 ... Ridge structure, 84 ... n-GaN
Contact layer, 86 ... n-side electrode.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsunori Yasushima             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F-term (reference) 5F073 AA14 AA45 AA74 CA07 CB02                       CB05 DA05 DA35 EA23

Claims (6)

[Claims] 1. A substrate comprising a striped ridge portion having a top portion in the same plane orientation as the main surface of the substrate on the main surface of the substrate, and epitaxially grown on the ridge portion of the substrate to form a film on the top of the ridge portion, A film is formed on the upper surface part having the same plane orientation as the main surface as the growth surface, on the side wall of the ridge portion, on the inclined surface portion having the growth surface with a predetermined plane orientation, and on the substrate main surface on the side of the ridge portion. A first GaN-based compound semiconductor layer having a flat portion whose growth surface has the same plane orientation as the main surface, and a substantially same shape on the first compound semiconductor layer along the first compound semiconductor layer. A GaN-based semiconductor laser device, comprising: a laminated structure of GaN-based compound semiconductor layers including an active layer. 2. The GaN-based semiconductor laser device according to claim 1, wherein the striped ridge portion is formed on a GaN-based compound semiconductor layer formed on the main surface of the substrate. 3. The main surface is a (0001) plane, the extension direction of the ridge is in the range of <1-100> ± 10 °, and the growth surface of the inclined surface is a (11-22) plane. The GaN-based semiconductor laser device according to claim 1 or 2. 4. The InGaN-based quantum well structure layer, wherein the active layer has an upper surface portion that functions as a light emitting region, and an inclined surface portion that is thinner than the upper surface portion and has a low light emitting property and does not substantially contribute to light emission. The upper clad layer is formed of an AlGaN-based compound semiconductor layer having an upper surface portion having a low electric resistance and functioning as a current injection region, and an inclined surface portion having a higher electric resistance than the upper surface portion and functioning as a current confinement region. 4. The Ga according to claim 1, wherein the GaN contact layer under the electrode is laminated on the upper clad layer in the same shape as the upper electrode.
N-based semiconductor laser device. 5. A method of epitaxially growing a GaN-based compound semiconductor layer on a stepped substrate having a striped ridge portion having a top portion in the same plane orientation as the main surface of the substrate on the main surface of the substrate, the method comprising: A top surface portion having a growth surface in the same plane orientation as the main surface, an inclined surface portion having a growth surface with a predetermined plane orientation formed on the sidewall of the ridge portion, and the substrate main surface on the side of the ridge portion. A step of epitaxially growing a GaN-based compound semiconductor layer, which is formed on the ridge portion of the substrate and has a flat portion having a growth surface in the same plane orientation as the main surface, and a step of epitaxially growing the GaN-based compound semiconductor layer Then, the growth conditions including at least the growth temperature and the V / III ratio of the source gas are adjusted to control the growth rate ratio of the upper surface portion and the inclined surface portion, and to adjust the ridge width and the ridge height of the ridge portion. Thus, an epitaxial growth method on a stepped substrate, characterized in that a GaN-based compound semiconductor layer having an upper surface portion having a desired film thickness and width and an inclined surface portion having a film thickness thinner than the upper surface portion is formed. 6. A stepped substrate having a striped ridge portion having a top portion having the same plane orientation as the (0001) plane main surface of the substrate and extending in an orientation range of <1-100> ± 10 °
A method for manufacturing an aN-based semiconductor laser device, comprising: a growth temperature of 800 ° C. or higher and 1040 ° C. or lower according to the epitaxial growth method on a stepped substrate according to claim 5.
An upper surface portion having a (0001) plane and a (11-
22) an active layer having an InGaN-based quantum well structure and an upper clad layer made of an AlGaN-based compound semiconductor layer having an inclined surface portion having a plane, and the active layer has an upper surface portion that functions as a light emitting region and an upper surface portion. The upper cladding layer has an inclined surface portion that is thinner and has a low light emitting property and does not substantially contribute to light emission. A method for manufacturing a GaN-based semiconductor laser device, characterized in that the GaN-based semiconductor laser device has a high inclined surface portion that functions as a current confinement region.