JPS61120487A - Semiconductor laser device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to semiconductor laser devices), particularly metal organic chemical vapor deposition (MOCVD), and molecular beam deposition (MBE).
The present invention relates to a semiconductor laser device manufactured using a crystal growth method having a non-equilibrium and balanced growth mechanism such as the method (method).

[Background of the invention]

In the semiconductor V-zer, a transverse mode control mechanism for stabilizing the internal oscillation mode is not available. In semiconductor lasers manufactured using the liquid phase epitaxy method, groove stripes are formed on the substrate, and C f3 p (Channeled
5ubstrata planer) v-the has been put into practical use. However, when a crystal growth method with a non-equilibrium growth mechanism such as MOCVD or MBE is used to grow on a similar substrate with groove stripes, a unique growth mechanism that maintains the shape of the substrate and grows. The active layer is bent, and an optical waveguide effect equivalent to that of a C8P laser cannot be expected, and crystal defects occur in the bent active layer, reducing reliability. Therefore, a structure in which a transverse mode control mechanism is provided in the grown layer above the active layer after flat growth up to the active layer is considered, an example of which is shown in FIG. This laser structure was described in App by J. J. Coleman et al.
ed Physics Letters, vol. 1980, p. 37, 262.

The manufacturing method of this laser is as follows:
GaAs buffer layer 2. n-GaAlAs crat layer 3
, active layer 4, I)-GaAIAS crat layer 5, n
- After the QaAs current confinement layer 6 is sequentially grown (by the MOCvD method), the upper current confinement layer 6 that performs V-laser oscillation is removed by seven etching layers and chemical etching, and then p
A -GaAs cladding layer 7 and a p-GaAs-871 layer 8 are sequentially grown by MOCVD. Next, the n-electrode 9,
A p-electrode 10 is formed. In this structure, the current constriction layer 6 causes current to flow concentrated in the light emitting region, and 2) the fundamental transverse mode is realized in the light absorption of the current confinement layer 6. However, this structure has a major drawback in its groove formation process. The conditions necessary for etching to form a groove are to completely remove the current confinement layer 6 and remove the 9-GaAlAs cladding layer 50.
Etching should be stopped as soon as the surface is exposed. For this purpose, a selective etching solution is suitable, in which the etching rate decreases as the molar ratio of t increases. An etching solution that satisfies this requirement is a mixed solution of ammonia solution and hydrogen peroxide.

However, the higher the molar ratio of ht, the slower the etching rate, which means that At is oxidized and A40. is formed and the etching rate decreases.

When the second growth is performed on this oxide (A40g), the growth interface (p-GaAIAS layer 5 and PGaAt
There is a drawback that device characteristics deteriorate due to abnormal growth or introduction of crystal defects between the As layers 7).

Furthermore, since transverse mode control is performed using light absorption in the current confinement layer 6, there is a drawback that internal loss increases and electricity-to-light conversion efficiency deteriorates.

[Purpose of the invention]

An object of the present invention is to provide a transverse mode control mechanism for a semiconductor laser device manufactured using a crystal growth method having a non-equilibrium growth mechanism such as MOCvD method or MBE method.

[Summary of the invention]

As described above, conventional semiconductor lasers manufactured using the MOCvD method and the MBE method have problems such as folding of the active layer9, abnormal growth during the second growth, or introduction of crystal defects. Therefore, it was necessary to devise a device structure in which each growth layer of a semiconductor laser is made flat and has a transverse mode control mechanism. The present invention relates to such a V-za structure. The present invention will be explained in detail using FIG. FIG. 2 shows GaA which is an example of the present invention.
This figure shows a cross-sectional structure of an s-GaAtAs semiconductor laser. This structure has rl-
()aAsAs rose 2f, n ()al-x klx
As cladding layer 11, undoped Gal + FA
A, As active layer 12, p-Gat-gAt, As cladding layer 13, n-Gat + II At@As current confinement/light reflection layer 14 are sequentially provided, and then n-Ga1- is formed in the portion corresponding to the light emitting region. @After selectively removing the AAAs layer 14 and forming trench stripes, f' Gal -v
This is a structure in which an ATVAs cladding layer 15.1) and a GaAS cap layer 8 are sequentially provided, and then an electrode 9.10 is formed. Here, A40 mole of each layer This relationship is y<xS
Setting it so that Z, v(u) is a void.

At this time, if the thickness of the p Ga[1A4As cladding layer 13 is set appropriately thin (~0.5 μm or less), the light emitted from the active layer 12 outside the groove stripe region becomes p Ga1
-iA4As cladding layer 13t- through, n G
A1-w people reach the disciple S layer 14. As a result, the light wave outside the groove stripe region is n -Gas -m A4
The low refractive index of the As layer 14 is felt, and the refractive index is effectively lower than that in the groove stripe region. Due to this refractive index difference, the transverse mode is stably guided. Furthermore, outside the groove stripe region, the p-Ga1-s layer As cladding layer 1
A current confinement layer is formed by the p-n inverse junction between the 3 and nQa,-,M layers 14, so that the current injection is concentrated within the trench stripes. This refractive index waveguide and current confinement mechanism stabilize the transverse mode even during high-power operation.

Furthermore, since the refractive index waveguide in this structure is realized only using the real part of the complex refractive index, the internal loss is small and the electrical-to-optical conversion efficiency is high.

Next, consider the invention from a manufacturing standpoint.

When forming groove stripes, it is important to completely remove the n-Ga1-, lume M layer 14 and to stop etching at the surface of the pG''+-5A4As layer 130.

In the case of the present invention, since z(u) is set, a selective etching solution with a lower etching rate can be applied as the molar ratio of At is smaller. An etching solution that satisfies this is hetamine acid or an aqueous solution thereof. This etching solution has an etching v-t of 10 when the molar ratio of At differs by 0.15.
There is a sufficient selection ratio. Therefore, the groove stripe etching is performed as p −Gat + *Al6 As
Being able to stop at the surface of layer 13 simplifies process control. Furthermore, since the etching of one groove stripe stops at I, which has a small molar ratio of At, no oxide film such as A408 is formed on the surface. No abnormal growth occurs, and good device characteristics can be obtained.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3.

Embodiment 1 FIG. 2 is a sectional view of a V-za device in which the present invention is also applied to an OaAZ 3-system semiconductor laser. As shown in FIG. 2, this structure consists of n-QaA,
s buffer layer (thickness 0.5 pm) 2, n-Ga
1-xAzxAs cladding layer (thickness 1.5μm) 11
, undoped Ga1-FAtFA$ active layer (thickness 0.0
6 μm) 12, p-Gat-gAtmAs cladding layer (
thickness 0.2 μm) 13, n-Ga 1-m, Lt
*A' Current confinement/light reflection layer 14 (thickness 0.6 μm)
grow sequentially. Here y=0.14, x=z=
0.45. It was set to u=0.60. This wafer
A photoresist mask with a window width of 4 μm is formed on top by photolithography, and using this as a mask, the n-Gao, 4KTO, sAs layer 14 is etched using a hydrofluoric acid etching solution (HF:H20=1:10). Selectively remove. At this time, n-() due to this etching solution
a,,4. α. -5As layer 14 etching V-) is approximately 1 μm/IIGI, while pGao, s s
Ato, as Etching V-) of the As layer 13 is 0
．． The selectivity is about 100 at O1μm/1trix.
Since it is about twice as large, the etching is pGao, s s A
16.4 SAS layer 130 surface test stop.

After this, a p-Gat-vAleA8 cladding layer (thickness 1.5 μm) 15 and a p-GaAs cap layer (thickness 0.5 μm) are formed.
3 μm) 8 were successively provided, electrodes 9 and 10 were formed, and the resonator was cut to a resonator length of 300 μm. Here V=0.45
It was set to The above is the configuration of this embodiment, and the operation of this embodiment will be explained below.

Outside the groove stripe region, the light generated in the active layer 12 is
9 Gao,s 5Ato, 4sA as thin as 0.2μm
n-Gao which passes through the s layer 13 and has a low refractive index.
, n Ato , s As reaches the layer 14. As a result, the light wave outside the groove stripe region is n Gao,4A
To, the low refractive index of the aAs layer 14 is felt, and the refractive index is effectively lower than in the groove stripe region. Since this refractive index difference is about 10-3 to 10''z, the transverse mode is stably guided.Furthermore, outside the groove stripe region, p G
ao, 4A4. sAsAlB12 Gao, ssA4
Since a current confinement layer is formed by the p-n reverse junction between the atAs layers 14, current injection is concentrated within the groove stripes.

In this example, an element that oscillated at a wavelength of 780 nm, a threshold current of 25 mA, and an optical output of 50 mwcw in the fundamental transverse mode could be obtained with good reproducibility. Furthermore, since abnormal growth and crystal defects are not generated at the second growth initiation interface, reliability is improved, and a long life of 10,000 hours was obtained in an accelerated life test with a constant light output of 70C and 40 mW.

Embodiment 2 FIG. 3 is a sectional view of a different embodiment of the present invention.
Buffer layer (thickness Q, 5 μm) 2, n-Gat + x
A3 cladding layer (thickness L5μff1) 11, undoped Gat-yAt, As active layer (thickness 0.06μm)
) 12, p-Ga1-ah film As cladding layer (thickness 0.
2 μm) 13, “G at -skt, As current confinement/light reflection layer (thickness 0.6 pm) 14, n-GaA
An s-selective etch mask layer (thickness of 0.2 μm or less) 16 is sequentially grown. Here y=0.14. x=z=0.4
5. It was set to u=0.60. This wafer
A photolithographic mask with a window of 1 mm and 4 μm was formed on the top by photolithography, and using this as a mask, the resist pattern was etched with n-GaA using a phosphoric acid etching solution.
After transferring to the S layer 16 and removing the resist,
In the same manner as in Example 1, n Gao
, 4^t6, 6 μm layer 14 is selectively removed and the remaining layer is grown.

The operation of this embodiment is exactly the same as that of the first embodiment.

The advantage of this example over Example 1 is that during the second growth, GaAtA, which is less likely to oxidize, is removed outside the groove stripe region.
s does not appear on the surface.

In this example, characteristics similar to those in Example 1 were obtained.

It should be noted that the present invention is not limited to the wavelength of around 0.78 μm as shown in the example, but similar results were obtained over the entire range in which continuous oscillation at room temperature is possible using a GaAtAS-based semiconductor V-za device with a wavelength of 0.68 to Q and 139 μm. . The semiconductor V-za device according to the present invention may be made of a V-za material other than GaAtAs, such as In.
The present invention can be similarly applied to GaASP-based and In()aP-based materials. In addition, the structure of the V-Z is not limited to the one based on the three-layer waveguide shown in each of the above embodiments, but also the LOC structure in which a light guide layer is provided adjacent to one side of the active layer, and the LOC structure in which a light guide layer is provided adjacent to one side of the active layer. 8CH with a light guide layer adjacent to each other
The present invention can be similarly applied to the GRI N-8CH tank structure in which the refractive index and forbidden band width of the optical guide layer are distributed in the film thickness direction. Furthermore, it is also effective for those whose active layer has a quantum well structure.
Similar results were also obtained in a structure in which the conductivity types were reversed in each of the above embodiments (a structure in which p was replaced with n and nt-p).

〔Effect of the invention〕

According to the present invention, when manufacturing a semiconductor laser using a crystal growth method having a non-equilibrium growth mechanism such as MOCvD method or MBE method, due to the shortcomings of the conventional transverse mode control mechanism, the second growth start interface rarely occurs. Abnormal growth and crystal defects can be removed, which has the effect of improving device characteristics, especially reliability. Furthermore, when forming groove stripes, a selective etching wave that does not form an oxide film on the surface can be introduced, making process control easier. As a result, a transverse fundamental mode with an optical output of 5 Qmw was obtained at a wavelength of 78 Qnm, and the average life was over 10,000 hours at an optical output of 40 mwcw and 70C. Therefore, it has become clear that the present invention is quite effective in achieving transverse mode stabilization and a highly reliable semiconductor V-za.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of a conventional transverse mode control type V-zer, FIG. 2 is a sectional view showing the configuration of an embodiment of the transverse mode control type laser according to the present invention, and FIG. 3 is a cross sectional view showing the configuration of a transverse mode control type laser according to the present invention. FIG. 7 is a sectional view showing the configuration of another embodiment. 1---n-GakS substrate, 2.''n-Ga A
S/<Tuffa layer, 3...n-GaAtAs cladding layer, 4...active layer, 5...p-GaAtAS cladding layer, 6.n-GaAS It current confinement layer 7-p-G
aAtAs cladding layer, sp-GaAS cap layer, 9...n electrode, 10...p electrode, 11-n
Gao, 5s Ato, 45 As cladding layer, 1
2...Undoped Gao, as Ato, l
4 As active layer, 130. . 9-Gao, s kLo-45As cladding layer, 14-nGao, a Ato, 6 As current confinement/light wave reflection layer, 15-I) Gao -s s Ato,
45 As cladding layer, 16 ・fl茗1fig￥r, z 躬

Claims (1)

[Claims] 1. On the first semiconductor region of the first conductivity type, at least the first
a second semiconductor layer of a conductivity type, a third semiconductor layer having a larger refractive index and a smaller forbidden band width than the second semiconductor layer, a second conductive layer having a smaller refractive index and a larger forbidden band width than the third semiconductor layer; After sequentially forming a fourth semiconductor layer of a first conductivity type and a fifth semiconductor layer of a first conductivity type having a smaller refractive index and a larger forbidden band width than the third and fourth semiconductor layers, the fifth semiconductor layer is etched. However, the fifth semiconductor layer is etched using an etching method that makes it difficult to etch the fourth semiconductor layer to provide groove stripes in which the fourth semiconductor layer is exposed, and then the fourth and third semiconductor layers having the groove stripes are etched. 5. A semiconductor laser device characterized in that a sixth semiconductor layer of a second conductivity type having a smaller forbidden band and a larger refractive index than at least the fifth semiconductor layer is provided on the fifth semiconductor layer. 2. In the semiconductor laser device according to claim 1, after the fifth semiconductor layer is sequentially provided and before etching, a semiconductor laser having a larger refractive index and a smaller forbidden band width than the third semiconductor layer is formed. After providing the seventh semiconductor layer of the first conductivity type, groove stripes are then formed by an etching method, in which a non-selective etching method is used to remove the seventh semiconductor layer; A semiconductor laser device characterized by being the same as described above. 3. In the semiconductor laser device according to claim 1 or 2, the third semiconductor layer has a thickness of one layer or more.
A semiconductor laser device characterized in that it is formed from a quantum well layer with a thickness of Å to 300 Å. 4. A semiconductor laser device according to any one of claims 1 to 3, characterized in that it has two or more stripes for laser oscillation.