JPH08186324A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a semiconductor laser which reduces an irregularity in an element characteristic and in which the light-emitting wavelength of an ordinary laser is absorbed by a current stop layer by a method wherein compositions of compound semiconductors for a lower clad layer, a first upper clad layer, a second upper clad layer, an active layer and the current stop layer are specified respectively. CONSTITUTION: In a semiconductor laser, a first conductivity type lower clad layer 2, an active layer 3, a first second conductivity type upper clad layer 4, a first conductivity type current stop layer 6 which is provided with a stripe- shaped opening part and a second conductivity type upper clad layer 8 are laminated sequentially on a first conductivity type GaAs substrate 1. Then, the lower clad layer 2, the first and second upper clad layers 4, 8 and the active layer 3 are composed of compound semiconductors whose composition formula is expressed by Alx Ga1-x As (where 0<=x<=1, but 0<=x<=0.3 for the active layer 3), and the current stop layer 6 is composed of a compound semiconductor whose composition formula is expressed by (Aly Ga1-y )z In1-z P [where (z) is about 0.5].

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a semiconductor laser. More specifically, it relates to a semiconductor laser using an AlGaAs compound semiconductor material and a method for manufacturing the same.

[0002]

2. Description of the Related Art Demand for AlGaAs semiconductor lasers is rapidly expanding as a light source for optical recording / reproducing such as compact discs and laser discs. In producing such a semiconductor laser, molecular beam growth (MB
Although it is effective to stack the respective semiconductor layers by the method E), a step of etching the current blocking layer in a stripe shape on the way to define a portion forming a current path by the semiconductor layers stacked thereon. Is required. As a method of re-growing the AlGaAs crystal layer without any special surface treatment after this etching step, there is a GaAs re-evaporation method, which is described in Applied Physics Vol. 54, pages 1208-1211. This will be described with reference to the sectional views according to the manufacturing process of FIGS.

In the first crystal growth step of FIG. 2A, n-type Al _s Ga _1-s A is formed on the n-type GaAs substrate 21, for example.
s lower clad layer 22 (for example, s = 0.6, Si concentration of about 5 × 10 ¹⁷ / cm ³ , thickness of about 1.3 μm), non-doped Al _u Ga _{1 -u} As active layer 23 (u = 0. 15, p-type Al _s Ga _{1 -s} As upper first cladding layer 24 (eg, s = 0.6, Be concentration about 1 ×).
10 ¹⁸ / cm ³ , thickness about 0.35 μm), n-type GaAs
Current blocking layer 25 (Si concentration 1 × 10 ¹⁸ / cm ³ , thickness about 0.4 μm), n-type Al _t Ga _{1 -t} As evaporation prevention layer 26
(T = 0.15, Si concentration about 1 × 10 ¹⁸ / cm ³ , thickness about 0.02 μm) and non-doped GaAs layer 27
(Thickness: about 0.02 μm) Each layer is sequentially grown by the MBE method.

Next, in the chemical etching step of FIG. 2B, this substrate is taken out from the MBE apparatus, and a stripe-shaped groove having a width of, for example, about 4 μm is formed with a sulfuric acid-based etching solution by a normal photo-etching step. At this time,
As in (b), the GaAs layer 25 having a thickness of about 0.1 μm is left as a surface protection layer, the wafer is washed, and M
Put in the BE device.

Now, the process proceeds to the thermal etching step of FIG. 2C, and before re-growth, a p-type Al _s Ga _1-s which is a surface protective layer is formed.
GaAs current blocking layer 2 on As upper first cladding layer 24
5 and Ga on the n-type Al _t Ga _1-t As evaporation prevention layer 26
The As layer 27 is heated to a high temperature while being exposed to the As molecular beam, and evaporated. The evaporation rate of GaAs at 740 ° C is about 2 μm.
/ H, but Al _x Ga _1-x As (x ≧ 0.15) is negligibly small, and only GaAs is selectively etched. Usually, the regrown wafer is heat-treated at 740 ° C. for about 15 minutes.

In this way, the GaAs layer on the surface is selectively etched to expose a clean AlGaAs surface.
In the second crystal growth step of (d), p-type Al _s Ga _1-s As
Upper second cladding layer 28 (eg, s = 0.6, Be
Concentration about 2 × 10 ¹⁸ / cm ³ , thickness about 1.3 μm), p ⁺ type GaAs cap layer 29 (Be concentration about 1 × 10 ¹⁹ / cm 3)
³ , thickness of about 0.6 μm) is successively grown. After that, an electrode material is vapor-deposited and cleaved to a cavity length of 250 μm to obtain a stripe type semiconductor laser.

[0007]

In such a conventional semiconductor laser, (1) since the current blocking layer is made of GaAs having a small energy gap, the light of the active layer is absorbed by this layer, and this energy is absorbed. The operating current becomes large due to the loss. (2) Since the re-evaporation method by the MBE method (method of re-evaporating the GaAs layer once grown) is used to manufacture this semiconductor laser, it is necessary to control the semiconductor substrate temperature with high accuracy, and the device is held. Is difficult. (3) Since a high temperature is required during this re-evaporation, there are problems such as deterioration of the active layer and the like, or variation in carrier distribution.

[0008]

The present invention is an internal stripe type semiconductor laser which can be manufactured without using the re-evaporation method and in which light absorption by the current blocking layer does not occur. That is, the semiconductor laser according to the present invention comprises a first conductivity type GaAs substrate, a first conductivity type lower cladding layer, and
An active layer, a second conductivity type upper first cladding layer, a first conductivity type current blocking layer having a stripe-shaped opening, and a second
A conductive upper second cladding layer is sequentially stacked,
The lower clad layer, the upper first and second clad layers,
Each of the active layers has a composition formula: Al _x Ga _1-x As (0 ≦ x <
1, where the active layer is composed of a compound semiconductor represented by 0 ≦ x ≦ 0.3), and the current blocking layer has a composition formula: (Al _v Ga _1-v ) _z In _1-z P ( z is about 0.
It is composed of a compound semiconductor represented by 5).

Here, the first conductivity type and the second conductivity type mean that when either n-type or p-type is the first conductivity type, the other p-type or n-type is the second conductivity type. Means there is.

Further, the value of x in at least a portion of the upper first cladding layer which is in contact with the current blocking layer is larger than that in the active layer and is 0.5 or less. It is preferable that it can be easily regrown.

Similarly, between the current blocking layer and the upper second cladding layer, the composition formula: Al _x G
A protective film made of a compound semiconductor of a _1-x As is provided, and the value of x is set to be larger than that in the active layer and 0.5 or less, so that the regrowth can be easily performed thereon by the MOVPE method. It is preferable to be able to.

The manufacturing method of the semiconductor laser according to the present invention is as follows.
(A) Composition formula: Al _x on a GaAs substrate of the first conductivity type
A compound semiconductor represented by Ga _1-x As (0 ≦ x <1, but 0 ≦ x ≦ 0.3 in the active layer) is laminated by changing the value of x appropriately, A step of sequentially forming a lower clad layer, an active layer, and an upper first clad layer of the second conductivity type, (b) (Al _v Ga _{1 -v} ) _z In _{1 -z} P (z is about 0.
5) a step of laminating a layer made of the first-conductivity-type compound semiconductor, (c) using an etching solution containing at least HCl, the (Al _v Ga _{1 -v} ) _z In _{1 -z} P ( z is about 0.5), a step of selectively etching a layer made of a compound semiconductor to form a current blocking layer having a stripe-shaped opening, (d) composition formula: Al _x Ga _{1- x} As
Secondly, stacking compound semiconductors represented by (0 ≦ x <1)
It includes a step of forming a conductive upper second cladding layer and a step of forming a cap layer made of (e) GaAs.

[0013]

In the semiconductor laser of the present invention, the current blocking layer is
It is made of (Al _v Ga _1-v ) _z In _1-z P (z is about 0.5) and is selectively etched by an HCl-based etching solution. The reproducibility of the stripes is improved, and the semiconductor laser of the present invention has less variation in element characteristics and is excellent in mass productivity. Further, the emission wavelength (700 nm ≦ λ ≦ 900 nm) of a normal AlGaAs laser is not absorbed in this current blocking layer. That is, energy loss does not occur and the operating current can be reduced.

[0014]

Next, one embodiment of the semiconductor laser of the present invention will be described in detail with reference to the drawings. FIG. 1 (a)-
(D) is sectional explanatory drawing which shows one Example of the semiconductor laser of this invention according to a manufacturing process.

In the step of FIG. 1A, n-type Al _s Ga _{1 -s} As (0.3) is formed on the surface of the first conductivity type, for example, the n-type GaAs substrate 1 whose main surface is the (100) plane. ≤s≤0.
8) Lower clad layer 2 (for example, s = 0.6, carrier concentration about 1 × 10 ¹⁸ / cm ³ , thickness about 1.2 μm, Se
Doped), undoped or n-type or p-type Al _u
Ga _1-u As (0 ≦ u ≦ 0.3, u <s) active layer 3 (eg u = 0.15, thickness about 0.07 μm), second conductivity type, eg p-type Al _s Ga _1-s As upper first cladding layer 4 (for example, s = 0.6, carrier concentration about 1
× 10 ¹⁸ / cm ³ , thickness about 0.3 μm, Be-doped),
p-type Al _t Ga _1-t As (u <t ≦ 0.5) upper first cladding layer protective film 5 (for example, t = 0.5, carrier concentration about 1 × 10 ¹⁸ / cm ³ , thickness about 0). 0.05 μm, Be-doped), n-type (Al _v Ga _1-v ) _z In _1-z P (0 ≦ v ≦
1, z is about 0.5) current blocking layer 6 (eg v = 0.
5, carrier concentration 2 × 10 ¹⁸ / cm ³ , thickness about 0.05
μm, Se-doped), n-type Al _w Ga _1-w As (u ≦ w ≦
0.5) Current blocking layer protective film 7 (for example, w = 0.5,
Carrier concentration about 2 × 10 ¹⁸ / cm ³ , thickness 0.05μ
Each layer of m and Se is sequentially grown on the n-type GaAs substrate 1 by MOVPE (Metal Organic Vapor Phase Epitaxy) method. In addition, _{z of} (Al _v Ga _1-v ) _z In _1-z P is about 0.5 and Ga
It is a value that is lattice-matched with the As substrate.

In the semiconductor laser of the present invention, the upper first cladding layer 4, the upper first cladding layer protective film 5, and the current blocking layer 6 are formed of a material having an energy band gap larger than that of the active layer 3. By doing so, the absorption of light in each of these layers can be prevented, and the luminous efficiency can be increased.

Next, in the step of FIG. 1B, the substrate is taken out of the growth chamber, a mask pattern having a width of, for example, about 3 μm is formed in the photoresist step, and the substrate is etched from the surface with this width. A stripe-shaped groove reaching the upper first cladding layer protective film 5 is formed. At this time, after the current blocking layer protective film 7 is removed with an H ₂ SO ₄ -based etching solution, the current blocking layer 6 is covered with, for example, HCl: H ₂ O.
It is selectively etched in about 20 seconds using an etching solution of = 1: 1. The etching selectivity at this time is good as shown in Table 1.

[0018]

[Table 1]

First upper portion exposed by this etching
On the current blocking layer protective film 7 covered with the clad layer protective film 5 and the resist film 10, both can be regrown by the MOVPE method without any special surface treatment thereafter.

Next, in the step of FIG. 1C, the resist film 12 is removed and washed, and then the substrate is again MOVPE.
Introduced into the process, the p-type Al _s Ga _1-s As upper second cladding layer 8 (for example, s = 0.6, carrier concentration about 5 × 10 5
¹⁸ / cm ³ , thickness 1.0 μm, Be-doped), p-type Ga
As cap layer 9 (for example, carrier concentration of about 2 × 10
¹⁹ / cm ³ and a thickness of about 1.6 μm) are crystal-grown on the entire surface.

Finally, in the step of FIG. 1D, the n-type GaAs substrate 1 is polished from the back surface, and the step up to FIG. 1C includes a semiconductor layer laminated on the surface of the substrate 1. The total thickness is about 60 μm. After that, the laminated body ohmic electrode 10 made of, for example, Ti / Au on the front surface of the substrate 1 and Au / Ge / Ni on the back surface,
11 are formed and cleaved into chips.

According to this embodiment, a semiconductor laser of low operating current can be obtained.

[0023]

As described above, the semiconductor laser according to the present invention includes steps such as an evaporation step after the current blocking layer is etched, in which the accuracy of controlling the temperature of the semiconductor substrate is delicate and a step due to high temperature. Therefore, it does not take time to hold the manufacturing apparatus, the crystallinity of the semiconductor layer such as the active layer deteriorates, and the carrier distribution does not change.
Mass production is possible at low cost with few processes. Further, since the current blocking layer is not made of a material having a small energy band gap and easily absorbing light such as GaAs which has been conventionally used, it is possible to easily obtain a semiconductor laser having good emission efficiency and a low operating current. be able to.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a semiconductor laser of an embodiment of the present invention according to a manufacturing process.

FIG. 2 is a cross-sectional explanatory view showing a conventional semiconductor laser according to a manufacturing process.

[Explanation of symbols]

 1 GaAs substrate 2 lower clad layer 3 active layer 4 upper first clad layer 5 upper first clad layer protective film 6 current blocking layer 7 current blocking layer protective film 8 upper second clad layer 9 cap layer

Claims (4)

[Claims] 1. A first conductivity type GaAs substrate, a first conductivity type lower clad layer, an active layer, and a second conductivity type upper first layer.
A clad layer, a current blocking layer of a first conductivity type having a stripe-shaped opening, and an upper second clad layer of a second conductivity type, which are sequentially laminated, and the lower clad layer, the upper first clad layer and the upper part Each of the second cladding layer and the active layer has a composition formula: Al _x Ga _1-x As (x is 0 ≦ x <1, provided that each layer is within the range of 0 ≦ x ≦ 0.3 in the active layer). Of a compound semiconductor represented by the formula: (Al _v Ga _1-v ) _z I
A semiconductor laser made of a compound semiconductor represented by n _{1 -z} P (z is about 0.5). 2. The semiconductor laser according to claim 1, wherein the value of x in at least a portion of the upper first cladding layer in contact with the current blocking layer is larger than that in the active layer and 0.5 or less. 3. A protective film made of a compound semiconductor having a composition formula: Al _x Ga _1-x As is further provided between the current blocking layer and the upper second cladding layer, and x in the protective film.
3. The semiconductor laser according to claim 1, wherein the value of is larger than that in the active layer and is 0.5 or less. 4. (a) On a GaAs substrate of the first conductivity type,
A compound semiconductor represented by a composition formula: Al _x Ga _1-x As (0 ≦ x <1, where 0 ≦ x ≦ 0.3 in the active layer) is laminated by appropriately changing the value of x, A step of sequentially forming a first conductivity type lower clad layer, an active layer, and a second conductivity type upper first clad layer, (b) (Al _v Ga _{1 -v} ) _z In _{1 -z}
A step of stacking a layer made of a compound semiconductor of the first conductivity type represented by P (z is about 0.5), (c) at least HCl
(Al _v Ga _1-v ) _z using an etching solution containing
A step of selectively etching a layer made of a compound semiconductor represented by In _1-z P (z is about 0.5) to form a current blocking layer having a stripe-shaped opening, (d) composition formula :
Stacking compound semiconductors represented by Al _x Ga _1-x As (0 <x <1) to form an upper second cladding layer of the second conductivity type, and (e) forming a cap layer made of GaAs A method of manufacturing a semiconductor laser including the steps of: