JP2001077473A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the aspect ratio of a semiconductor laser in a low threshold current by a method where a striped aperture is formed, in such a way as to make a substrate, an n-type layer and a current constricting layer consisting of a high-meting point metal layer penetrate and a quantum well active layer is formed on the striped aperture. SOLUTION: An AlN buffer layer 2 and an n-type GaN layer 3 are grown on a sapphire substrate 1 in a first crystal growth by an organometallic vapor growth method, and thereafter a current-constricting layer 4 consisting of a tungsten layer is deposited on the layer 3. After that, A striped aperture 5 is formed in such a way as to make the layer 4 penetrate. Then a first clad layer 6, a first light guide layer 7, a multi-quantum well active layer 8, a cap layer 9, a second light guide layer 10, a second clad layer 11 and a contact layer 12 are grown in the order in a second crystal growth. Lastly, a p-type electrode 13 is formed on the striped aperture 5, and an n-type electrode 14 is formed on the surface of the layer 3 etched, until one part of the layer 3 is exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN semiconductor laser expected to be applied to the field of optical information processing and the like.

[0002]

2. Description of the Related Art In recent years, large-capacity optical disk devices such as digital video disks have been put into practical use, and the capacity is going to be further increased in the future. As is well known, shortening the wavelength of a semiconductor laser serving as a light source for reading and writing is one of the most effective means for increasing the capacity of an optical disk device. Therefore, a semiconductor laser for a digital video disk currently on the market has a wavelength of 650 nm made of an AlGaInP-based material. It is considered.

Semiconductor lasers used for optical disks are required to have long life and low threshold current operation, as well as stable single transverse mode operation, low astigmatic difference, low noise and low aspect ratio. At present, a 400 nm band semiconductor laser satisfying all these characteristics has not been realized.

Conventionally, a single transverse mode type GaN-based semiconductor laser
The one with the cross-sectional structure of the element shown in Fig. 3 is proposed as
Have been. First crystal growth on sapphire substrate 101
GaN buffer layer 102, n-GaN layer 103, p-G
The aN current confinement layer 104 is grown, and once removed from the growth apparatus.
After the opening, the stripe-shaped opening 105 _Two
Formed by reactive ion etching with gas
You. The striped openings 105 are at least p-
Must completely penetrate GaN current confinement layer 104
Absent.

Next, the wafer is again introduced into the crystal growing apparatus, and the second
N-AlGaN first cladding layer 106,
n-GaN first optical guide layer 107, Ga _1-x In _x N / G
_{a 1- y In y N (0} <y <x <1) multi-quantum well active layer 108 made of, p-AlGaN cap layer 109, p-G
An aN second light guide layer 110, a p-AlGaN second cladding layer 111, and a p-GaN contact layer 112 are grown.

Finally, a p-electrode 113 made of, for example, Ni / Au is formed directly above the stripe-shaped opening 105, and a p-electrode 113 made of, for example, Ti / Al is formed on a part of the surface etched until the n-GaN layer 103 is exposed. An n-electrode 114 is formed,
A single transverse mode GaN-based semiconductor laser whose sectional structure is shown in FIG. 3 is manufactured.

In this device, the n-electrode 114 is grounded,
When a voltage is applied to the p-electrode 113, the multiple quantum well active layer 10
A hole is formed from the p-electrode 113 side toward
Electrons are injected from the 114 side, and the multiple quantum well active layer 108
An optical gain is generated in the device, causing laser oscillation. The bias at the time of driving the laser is applied to the p-GaN current confinement layer 104.
When the junction between the n-AlGaN first cladding layer 106 and the n-AlGaN first cladding layer 106 is reverse-biased, current concentrates only on the stripe-shaped opening 105 where the p-GaN current confinement layer 104 does not exist.

On the other hand, since the multiple quantum well active layer 108 formed on the stripe-shaped opening 105 has a bent shape as shown in FIG. 3, a difference in refractive index occurs in the growth layer in the horizontal direction. The laser beam is also stably confined in the multiple quantum well active layer 108 immediately above the stripe-shaped opening 105. For this reason, the distribution of the injected carriers and the light substantially match, and oscillation at a low threshold current density becomes possible. Also,
As described above, since the refractive index waveguide structure has a refractive index difference in the direction parallel to the growth layer, the optical mode is stable, and a high-performance semiconductor laser with a very small astigmatic difference can be realized.

[0009]

However, there is a problem which is extremely difficult to avoid when actually manufacturing the single transverse mode GaN-based semiconductor laser. In FIG. 3, a p-GaN current confinement layer 104 is used, but GaN is a material having a relatively large refractive index. That is, n
The refractive index is higher than that of the first AlGaN cladding layer 106; Since the multiple quantum well active layer 108 is bent, FIG.
As shown in the refractive index distribution in the direction horizontal to the growth layer, the light is confined by the difference in the refractive index from the n-AlGaN first cladding layer 106. However, n-AlGaN
Further outside the first cladding layer 106, n-AlGaN first
When the p-GaN current confinement layer 104 having a higher refractive index than the cladding layer 106 is present, light is emitted from the p-GaN current confinement layer 104.
And the light confinement in the multiple quantum well active layer 108 is significantly reduced. This is particularly noticeable in a narrow stripe structure with a stripe width of 3 μm or less.

When light confinement in the multiple quantum well active layer 108 is reduced, characteristics unfavorable for application as a light source for an optical disk, such as an increase in the threshold current and the aspect ratio of the beam divergence angle, are obtained.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional single transverse mode GaN-based semiconductor laser, and has a stable single transverse mode operation, a low aspect ratio, An object of the present invention is to provide a high performance single transverse mode GaN-based semiconductor laser such as a low threshold current.

In the present invention, a high melting point metal such as W, Ta, or Mo having a high light absorption, or a low refractive index S is added to the current confinement layer.
A dielectric material such as iO ₂ , SiN, or Al ₂ O ₃ is used to enhance light confinement in an active layer bent in the horizontal direction. As a result, stable refraction with a low threshold current and a small aspect ratio is achieved. It is possible to realize a single transverse mode GaN-based semiconductor laser using index guided wave.

That is, the present invention provides a substrate, an n-type layer,
A semiconductor laser comprising a current confinement layer made of a high melting point metal, a stripe-shaped opening penetrating the current confinement layer, and a quantum well active layer formed on the stripe-shaped opening.

The refractory metal is preferably a metal that does not contaminate the crystal growth furnace, for example, any one of W, Ta, and Mo.

Further, according to the present invention, a substrate, an n-type layer, a current confinement layer made of a dielectric, a stripe-shaped opening penetrating the current confinement layer, and a quantum aperture formed on the stripe-shaped opening are provided. A semiconductor laser including a well active layer.

The dielectric material is SiO ₂ , SiN, Al ₂ O which is a dielectric material having a low refractive index and being stable with respect to the crystal growth temperature.
Preferably, any one of the _three types is used.

Further, the present invention is the above-described semiconductor laser having a quantum well active layer bent along the stripe-shaped opening.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view of a device of a single mode GaN quantum well semiconductor laser showing Embodiment 1. An AlN buffer layer 2 and an n-GaN layer 3 are grown by a first crystal growth on a (0001) sapphire substrate 1 by a metal organic chemical vapor deposition method. Is deposited to a thickness of about 1 μm by vacuum evaporation.
Thereafter, a stripe-shaped opening 5 having a width of 2 μm is formed by, for example, ion milling. The stripe-shaped opening 5 must completely penetrate at least the current confinement layer 4 made of tungsten.

Next, it is again introduced into the crystal growth apparatus, and the second
N-Al_0.07Ga _0.93N first cladding
Layer 6, n-GaN first light guide layer 7, Ga_1-xIn_xN
/ Ga_1-yIn_yMultiweight consisting of N (0 <y <x <1)
Subwell active layer 8, p-Al_{0. 08}Ga_0.92N cap layer 9
 , P-GaN second light guide layer 10, p-Al_0.07Ga_0.
93An N second cladding layer 11 and a p-GaN contact layer 12 are formed.
Lengthen.

Finally, a p-electrode 13 made of, for example, Ni / Au, and a part of the n-G
An n-electrode 14 made of, for example, Ti / Al is formed on the surface etched until the aN layer 3 is exposed.

The multiple quantum well active layer 8 has a thickness of, for example, 3n.
m Ga _0.9 In _0.1 N quantum well layer and 9 nm Ga _0.97
And an In _0.03 N barrier layer. Also, n-Al laminated on the current confinement layer 4 made of tungsten
The crystal layers subsequent to the _0.07 Ga _0.93 N first cladding layer 6 are polycrystalline and have high resistance. Therefore, a current is selectively injected into the multiple quantum well active layer 8 immediately above the stripe-shaped opening 5.

The light generated in the multiple quantum well active layer 8 is
When viewed in the vertical direction, the n-GaN first light guide layer 7, the multiple quantum well active layer 8, the p-Al _0.08 Ga _0.92 N cap layer 9
And the p-GaN second light guide layer 10 are particularly strongly confined in the four layers, but the difference in refractive index also occurs in the direction horizontal to the growth layer due to the step. The width of the bent portion 17 in the multiple quantum well active layer 8 is about 1.5 μm, and the refractive index waveguide structure has an effective stripe width.

In the case of this embodiment, since the narrow stripe structure is used, the light in the horizontal direction spreads to the current confinement layer 4 made of tungsten. Loss waveguide action occurs, and the effect of confining light to the multiple quantum well active layer 8 appears more strongly.
% Is obtained. Therefore, stable single transverse mode with low threshold current, low aspect ratio, etc.
High performance suitable for an optical disk light source can be realized. Further, even when the multiple quantum well active layer 8 has no bent portion 17 and is flat, the same effect can be obtained as long as the refractive index difference is caused by the current confinement layer 4 from tungsten.

Embodiment 2 FIG. 2 is a cross-sectional view of a device of a single mode GaN-based quantum well semiconductor laser showing Embodiment 2;
The current confinement layer was an SiO ₂ current confinement layer. An SiO ₂ current confinement layer 24 is deposited to a thickness of about 1 μm by vacuum evaporation. Thereafter, a stripe-shaped opening 25 having a width of 2 μm is formed by dry etching using, for example, CF ₄ . The opening 25 in the form of a stripe has at least Si
The O ₂ current confinement layer 24 must be completely penetrated.

Since the SiO ₂ current confinement layer 24 is an insulator, the current is applied to the multiple quantum well active layer immediately above the stripe-shaped opening 25.
28 is selectively injected. The light generated in the multiple quantum well active layer 28 is, when viewed in the vertical direction, the n-GaN first optical guide layer 27, the multiple quantum well active layer 28, and the p-Al _0.08 Ga _0.92 N
The cap layer 29 and the p-GaN second light guide layer 30 4
Although the layer is particularly strongly confined in the layer, the difference in refractive index also occurs in the direction horizontal to the growth layer due to the step. The width of the bent portion 37 in the multiple quantum well active layer 28 is about 1.5 μm,
This is a refractive index waveguide structure having an effective stripe width.

In the case of this embodiment, the narrow since the stripe structure is used light in the horizontal direction is also spread to the SiO ₂ current blocking layer 24, since the SiO ₂ current confinement layer 24 is a low refractive index material, a multiple quantum well The light confinement effect in the layer 28 appears more strongly. As a result, a light confinement coefficient of 90% or more is obtained.

Even when the multiple quantum well active layer 28 is flat without the bent portion 37, the same effect can be obtained if the refractive index difference is generated by the SiO ₂ current confinement layer 24.

[0029]

According to the present invention, a high-performance short-wavelength semiconductor laser having a low threshold current density and a single transverse mode, a low aspect ratio, etc., suitable for a light source for an optical disk can be realized.

[Brief description of the drawings]

FIG. 1 is an element cross-sectional view of a GaN-based single transverse mode semiconductor laser shown in Example 1.

FIG. 2 is a sectional view of a GaN-based single transverse mode semiconductor laser according to a second embodiment;

FIG. 3 is a sectional view of a conventional GaN-based single transverse mode semiconductor laser.

4 is a diagram showing a refractive index distribution in a direction horizontal to a growth layer of the conventional example shown in FIG.

[Explanation of symbols]

1,21 (0001) sapphire substrate 2,22 AlN buffer layer 3,23 n-GaN layer 4,24 W, SiO ₂ current confinement layer 5,25 striped opening 6,26 n-Al _0.07 Ga _0.93 N first cladding layer 7, 27 n-GaN first optical guiding layer _{8,28 Ga 1-x In x n} / Ga 1-y In y n multi quantum well active layer 9, 29 p-AlGaN cap layer 10, 30 p- GaN second light guide layer 11,31 p-Al _0.07 Ga _0.93 N second cladding layer 12,32 p-GaN contact layer 13,33 p electrode 14,34 n electrode 17,37 bent portion of active layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Motoaki Iwatani 702 F, Omaki, Omaki, Sobue-cho, Nakajima-gun, Aichi Prefecture 5F073 AA20 AA45 AA51 AA55 CA07 CB05 CB07 DA05 DA26 EA23

Claims (5)

[Claims] 1. A substrate, an n-type layer, a current confinement layer made of a refractory metal, a stripe-shaped opening penetrating the current confinement layer, and a quantum well active layer formed on the stripe-shaped opening. A semiconductor laser comprising: 2. The semiconductor laser according to claim 1, wherein said refractory metal is one of W, Ta, and Mo. 3. A substrate, an n-type layer, a current confinement layer made of a dielectric, a stripe-shaped opening penetrating the current confinement layer, and a quantum well active layer formed on the stripe-shaped opening. Semiconductor laser comprising: 4. The dielectric material is SiO ₂ , SiN, Al ₂ O ₃
2. The semiconductor laser according to claim 1, wherein the semiconductor laser is any one of the following. 5. The semiconductor laser according to claim 1, further comprising a quantum well active layer bent along the stripe-shaped opening.