JPH03238886A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable attainment of a semiconductor laser device which has no regenerative growth interface in an active region, by forming a ridge by etching, by forming a diffraction grating on a face in proximity to an active layer exposed and by making a crystal layer grow thereon by an MOCVD method. CONSTITUTION:A contact layer 7 is provided only on the top part of a first clad layer 6, and a diffraction grating 10 is formed on the surface of a guide layer being located on the opposite sides of the first clad layer 6 and not being in contact with this first clad layer 6. A second upper clad layer 8 of a first or second conductivity type being in contact with the diffraction grating 10 and having about the same composition as the first upper clad layer 6 is provided, and a current block layer 9 of a first conductivity type being in contact with this second upper clad layer 8 and having a forbidden band width being the same with or smaller than one of an active layer 3 is provided. According to this constitution, a semiconductor laser device having no recrystallization interface in an active region and being provided with the active layer 3 being flat is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor laser device, and particularly relates to a new and useful distributed feedback type semiconductor laser device.
The present invention relates to a laser device and a manufacturing method thereof.

[Conventional technology]

FIG. 3 shows, for example, Applied Physics Le
21 is a perspective view showing a DFB laser having a conventional loss guide mechanism described in tter Vol. 53, No. 7, pages 550 to 552, in which 21 is an n-type GaAs substrate;
22 is n-type A 1 o, rsG ao, ssA
S layer, 23 is a diffraction grating, 24 is an n-type GaAs layer, 25 is an n-type A 10.33G a 0.6? A S lower cladding layer, 26 is n-type A 1 o, osG a O, G14
AS active layer, 27 is P type A1o, 33G a 0.
8? 28 is an n-type GaAs contact layer, 29 is a 5iO- film, 30 is a ■-type groove, and 31 is a Zn diffusion region.

Next, a conventional manufacturing method will be explained with reference to FIGS. 4(a) to 4(e).

First, as shown in FIG. 4(a), as a first crystal growth step, A 1 o, rsG a o, and 22 asAs layers are formed. Next, as shown in FIG. 4(b),
A diffraction grating 23 is formed on the surface of the lo, rsGao8sA S layer 22 by ordinary interference exposure and chemical etching.

Next, as shown in FIG. 4(C), as a second crystal growth step, a GaAs layer 24 is formed to cover the diffraction grating 23.
grow.

Thereafter, as shown in FIG. 4(d), a square groove 30 having a V-shaped cross section is formed so as to reach the substrate 1 by selective chemical etching using a photolithography technique.

Next, as shown in FIG. 4(e), as a third crystal growth step, each layer from the lower cladding layer 25 to the contact layer 2 is grown by liquid phase epitaxy (LPE method).

Furthermore, an Si 02 film 29 with striped openings
Using (FIG. 3) as a mask, Zn is diffused to form a Zn diffusion region 31 and a current path. And finally,
Although not shown in the figure, after metal electrodes are formed on the front and back surfaces, each chip is separated to complete a device as shown in FIG. 3.

Next, the operation will be explained.

When a voltage is applied between the metal electrodes, a current confined by the Zn diffusion region 31 is injected into the active layer 26 and light emission occurs. The light is applied to the lower cladding layer 25. The light is guided by a waveguide formed by an effective refractive index distribution caused by the refractive index difference between the upper cladding layer 27 and the active layer 26 and the loss near the V-shaped groove 30, and oscillates as a laser. The oscillation wavelength is the diffraction grating 23
It becomes a single wavelength determined by the pitch of.

[Problem to be solved by the invention]

Since the conventional GaAs-based DFB laser is constructed as described above, the process is extremely complicated because it requires three crystal growth steps. Furthermore, the third crystal growth must be performed using the conventional LPE method because it is necessary to bury the V-shaped groove 30, planarize it, and form a flat active layer. Metalorganic chemical vapor deposition (MOCVD) is attracting attention as an excellent crystal growth method.
However, there is a problem in that vapor phase growth methods such as the method cannot be applied because it is difficult to fill and planarize trenches.

This invention was made to solve the above-mentioned problems, and all layers are grown using a vapor phase growth method, and moreover, it can be formed in a relatively simple process with only two crystal growth steps. An object of the present invention is to obtain a semiconductor laser device and a method for manufacturing the same.

[Means for Solving the Problems] A semiconductor laser device according to claim (1) of the present invention includes at least a lower cladding layer of a first conductivity type, an active layer, A guide layer of a second conductivity type and having a forbidden band width and a refractive index between the values of the active layer and the lower cladding layer.

A first upper cladding layer that is in contact with a part of this guide layer, has a ridge-like cross-sectional shape of the second conductivity type, and extends in a stripe shape in the direction of the resonator, and a contact layer that is provided only on the top of this first upper cladding layer. A diffraction grating is formed on the guide layer surface on both sides of the first upper cladding layer that is not in contact with the first upper cladding layer, and a diffraction grating is formed on the guide layer surface that is not in contact with the first upper cladding layer, and a diffraction grating that is in contact with the diffraction grating has the same extent as the first upper cladding layer. a second upper cladding layer of a first conductivity type or a second conductivity type having a composition, and in contact with this second upper cladding layer, a first A conductive type current blocking layer is provided.

Further, in the method for manufacturing a semiconductor laser device according to claim (2) of the present invention, on a semiconductor substrate having a first conductivity type,
At least a lower cladding layer and an active layer of a first conductivity type,
a step of sequentially forming a guide layer, a first upper cladding layer, and a contact layer which are of a second conductivity type and whose forbidden band width and refractive index are between those of the active layer and the lower cladding layer; A step of forming a mask extending in a stripe shape in the direction of the resonator, a step of etching away the contact layer and the first upper cladding layer other than the lower part of the mask to expose the surface of the guide layer; forming the diffraction grating on the surface of the guide layer, and using the mask as a mass for selective growth, forming a second upper cladding layer having the same composition as the first upper cladding layer on the guide layer having the diffraction grating; and a step of sequentially selectively growing a current blocking layer, and a step of removing the mask.

[Function] In claim (1) of the present invention, a ridge is formed by etching, a diffraction grating is formed on a surface close to the exposed active layer, and a crystal layer is grown thereon by MOCVD. A semiconductor laser device is obtained in which no regrowth interface exists within the region.

In addition, in the invention of claim (2), the diffraction grating is formed on the surface close to the active layer exposed by etching for ridge formation, and the cladding layer is grown in the second buried growth, so only two times are required. A semiconductor laser device can be manufactured by crystal growth using a relatively simple process overall.

〔Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the semiconductor laser device of the present invention, in which 1 is an n-type GaAs substrate, 2 is an n-type A substrate 10.
I G ao, s A S lower cladding layer, 3 is undoped A 1 o, + i G a o, as As active layer, 4 is P type A lo, s G ao, s A S carrier confinement layer, 5 is P type A l 6. *Gao,
a A S guide layer, 6 is P type A 1 o, s Ga
o, s A S first upper cladding layer, 7 a P-type GaAs contact layer, 8 a P-type Alo, sGa. s A s second
In the upper cladding layer, 9 is an n-type GaAs current blocking layer, 10 is a diffraction grating, and 11 is a metal electrode.

Next, the manufacturing process of the semiconductor laser device of the above example will be carried out in a second manner.
The explanation will be given according to figures (a) to (d).

First, as shown in FIG. 2(a), as a first crystal growth step, each layer from the lower cladding layer 2 to the contact layer 7 is sequentially grown on the substrate 1 by MOCVD.

Next, a striped insulating film having a width of about 2 to 5 μm, for example, a SiOz film 12, is formed.

Next, as shown in FIG. 2(b), the contact layer 7 is etched by chemical etching using the Sin and Pus 12 as a mask.
Then, the first upper cladding layer 6 is removed to form a ridge and the surface of the guide layer 5 is exposed. As the etchant in this case, for example, a mixture of sulfuric acid and hydrogen peroxide can be used.

Next, as shown in FIG. 2(C), the exposed guide layer 5
A diffraction grating 10 is formed on the surface by interference exposure and chemical etching. As the etchant in this case, for example, a mixed solution of phosphoric acid and hydrogen peroxide can be used.

Next, as shown in FIG. 2(d), in the second crystal growth step, 5iOi was used as a mask for ridge formation.
The film 12 is now used as a selective growth mask and the diffraction grating 1
A second upper cladding layer 8 and a current blocking layer 9 are selectively buried and grown on the guide layer 5 on which the layer 0 is formed by MOCVD.

After removing the Sin film 12, metal electrodes 11 are formed on the front and back surfaces by vacuum evaporation or the like, and finally, each chip is separated to complete the device shown in FIG.

Thus, according to this embodiment, only two MOCVs are required.
By crystal growth using the D method, it can be produced through relatively simple steps.

Next, the operation will be explained.

This operation is similar to the conventional example, but current confinement is achieved by the effect of the current blocking layer 9, and current flows through the ridge-shaped portion (first upper cladding layer 6 and contact layer 7). Since there is no regrowth interface on the AlGaAs in this current path, no problem arises in terms of electrical characteristics. Further, the lateral waveguide of light is also performed by a so-called loss guide mechanism caused by light absorption by the current blocking layer 9, and stable operation is possible up to high output. Since the laser beam is reflected by the diffraction grating 10 on both sides of the light distribution, it oscillates at a single wavelength defined by the pitch of the diffraction grating 10. Furthermore, in the case of the above example,
Since there are few regrowth interfaces on AlGaAs with a high AlAs composition in the active region, reliability problems do not occur.

Although the carrier confinement layer 4 in the above embodiment is provided to effectively confine injected carriers within the active layer 3, it may not necessarily be necessary depending on the design of the device.

Further, although the second upper cladding layer 8 is of P type, it may be of N type. In this case, current blocking is performed not only with the current blocking layer 9 but also with the second upper cladding layer 8.

In addition, although GaAs and AlGaAs are shown as materials, the materials are not limited to these.
For example, (AIGa)InP.

GaInP, InGaAsP, InP, etc. may also be used.

[Effects of the Invention] As explained above, the invention of claim (1) of the present invention provides at least a lower cladding layer, an active layer, and a second conductive layer of the first conductive type on the semiconductor substrate of the first conductive type. a guide layer having a forbidden band width and a refractive index between those of the active layer and the lower cladding layer;
A first upper cladding layer having a conductivity type, having a ridge-like cross-sectional shape and extending in a stripe shape in the direction of the resonator, and a contact layer provided only on the top of the first upper cladding layer,
A diffraction grating is formed on the surface of the guide layer not in contact with the first upper cladding layer on both sides of the first upper cladding layer, and a second guide layer having a composition similar to that of the first upper cladding layer is formed in contact with the diffraction grating. a second upper cladding layer of the first conductivity type or the second conductivity type, and in contact with the second upper cladding layer, the first conductivity layer has a forbidden band width that is the same as or smaller than the forbidden band width of the active layer.
Since the conductive current blocking layer is provided, a semiconductor laser device having a flat active layer without a recrystallization interface in the active region can be obtained.

Further, the invention of claim (2) provides a semiconductor substrate having a first conductivity type, at least a lower cladding layer and an active layer of the first conductivity type, a second conductivity type, and a forbidden band width and a refractive index. A step of sequentially forming a guide layer, a first upper cladding layer, and a contact layer having a value between the active layer and the lower cladding layer, and forming a mask extending in a stripe shape in the direction of the resonator on a part of the surface of the contact layer. a step of etching away the contact layer other than the lower part of the mask and the first upper cladding layer to expose the surface of the guide layer; and a step of forming a diffraction grating on the exposed surface of the guide layer. , using the mask as a mass for selective growth, sequentially forming a second upper cladding layer and a current blocking layer having the same composition as the first upper cladding layer on the guide layer having the diffraction grating;
The semiconductor laser device is a highly reliable semiconductor laser device having a stable loss guide mechanism, which is a relatively simple process that requires only two steps of vapor phase growth such as MOCVD, since it consists of a selective filling growth step and a step of removing the mask. There is an effect that can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a perspective view showing the manufacturing process of the semiconductor laser device of the present invention, and FIG. 3 is a perspective view showing a conventional semiconductor laser device. , FIG. 4 is a perspective view showing the manufacturing process of a conventional semiconductor laser device. In the figure, 1 is a GaAs substrate, 2 is a lower cladding layer, and 3 is a GaAs substrate.
is an active layer, 4 is a carrier confinement layer, 5 is a guide layer, 6
1 is a first upper cladding layer, 7 is a contact layer, 8 is a second upper cladding layer, 9 is a current blocking layer, and 10 is a diffraction grating. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) On the semiconductor substrate of the first conductivity type, at least the first
a lower cladding layer of a conductivity type, an active layer, a guide layer of a second conductivity type and whose forbidden band width and refractive index are between the values between the active layer and the lower cladding layer, in contact with a part of the guide layer,
The second conductivity type has a ridge-like cross-sectional shape, a first upper cladding layer extending in a stripe shape in the direction of the resonator, and a contact layer provided only on the top of the first upper cladding layer. A diffraction grating is formed on the surface of the guide layer that is not in contact with the first upper cladding layer on both sides of the cladding layer, and a first conductivity type or It has a second upper cladding layer of a second conductivity type, and in contact with the second upper cladding layer, a current blocking layer of a first conductivity type having a forbidden band width that is the same as or smaller than the forbidden band width of the active layer. A semiconductor laser device characterized in that: (2) on a semiconductor substrate having a first conductivity type, at least a lower cladding layer of the first conductivity type, an active layer, and a second conductivity type;
and a step of sequentially forming a guide layer, a first upper cladding layer, and a contact layer whose forbidden band width and refractive index are between those of the active layer and the lower cladding layer, and forming a resonator on a part of the surface of the contact layer. a step of forming a mask extending in a stripe shape in the direction; a step of etching away the contact layer and the first upper cladding layer other than the lower part of the mask to expose the surface of the guide layer; forming a diffraction grating; using the mask as a mask for selective growth, sequentially forming a second upper cladding layer and a current blocking layer having the same composition as the first upper cladding layer on the guide layer having the diffraction grating; . A method of manufacturing a semiconductor laser device, comprising the steps of selectively implanting and growing the mask, and removing the mask.