JPH04324689A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the temperature depending characteristic of a semiconductor laser by performing heat treatment on a laminated substrate twice after the time when an oscillation layer containing an n-type clad layer, active layer, and p-type clad layer respectively composed of AlGaInP compound semiconductors are formed on an n-type semiconductor substrate and when a p-type cap layer is formed on a block layer. CONSTITUTION:A buffer layer 2, n-type clad layer 3, active layer 4, p-type clad layer 5, contact layer 6, and protective layer 12 are successively formed on one main surface 1a of a substrate 1 and the laminated substrate thus obtained is heat-treated in a heating device. Then, after forming a stripe-like SiO2 film 16 on the laminated surface of the substrate 1, a stripe-like ridge 7 is formed by etching the layers 12, 6, and 5 by using the film 16 as a mask. After forming the ridge 7, an n-type block layer 8 is grown on the laminated surface and a p-type cap layer 9 is formed on the layer 8. Then the laminated substrate thus obtained is again heat-treated. After the heat treatment, a p-side and n-side electrodes 10 and 11 are respectively formed on the layer 9 and the other main surface 1b of the substrate 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an AlGaInP semiconductor laser.

0002

2. Description of the Related Art AlGaInP has a wavelength in the 0.6 μm band and is used as a material for visible light semiconductor lasers.

FIG. 1 shows such an AlGaInP semiconductor laser, which is described, for example, in the proceedings of the 38th Applied Physics Conference, 30p-D-10, page 1001.

In the figure, (1) is a substrate made of n-type GaAs, which has a main surface inclined from the (100) plane to the [011] direction.

(2) is a buffer layer made of n-type Ga0.5In0.5P, (3) is n-type (AlyGa1-y)0
．． 5In0.5P n-type cladding layer, (4) undoped (AlxGa1-x) 0.5In0.5P active layer, (5) p-type (AlyGa1-y) 0.5
p-type cladding layer made of In0.5P, (6) is p-type G
The contact layer is made of a0.5In0.5P, and these layers are sequentially laminated on the main surface of the substrate (1) using the well-known MOCVD method.

(7) is a striped ridge extending in the direction of the laser resonator, and is a striped ridge extending from the surface of the contact layer (6) to
It is formed by selectively etching away the inside of the mold cladding layer (5).

Reference numeral (8) denotes a block layer made of n-type GaAs, which is formed on the exposed p-type cladding layer (5) and on the contact layer (6) near the end face of the laser resonator. That is,
Such a semiconductor laser has a structure in which a current injection region (A) is formed inside a laser resonator and a current non-injection region (B) is formed near the end facet.

Reference numeral (9) is a cap layer made of p-type GaAs formed on the block layer (8) and the exposed contact layer (6).

(10) is a p-side electrode formed on the cap layer (9), and (11) is an n-side electrode formed on the other main surface of the substrate (1).

0010

[Problem to be solved by the invention] This type of AlGaInP
In comparison with AlGaAs-based semiconductor lasers, temperature-dependent characteristics such as maximum oscillation temperature are lower in the AlGaAs-based semiconductor lasers, and this poses a major problem for practical use. This is because the barrier difference between the active layer and the p-type cladding layer is small, and carriers (especially electrons) cannot be effectively confined within the active layer.

Methods for increasing such a barrier difference include a method of increasing the Al composition ratio of the p-type cladding layer to widen the band gap, and a method of increasing the carrier concentration of the cladding layer.

However, in AlGaInP,
When the Al composition ratio y to Ga is 0.7, the band gap becomes maximum, and even if the Al composition ratio is further increased, a larger band gap cannot be obtained.

Therefore, it is desirable to increase the bandgap of the cladding layer as well as its carrier concentration, but the amount of dopant incorporated into the layer tends to be saturated at a certain point, and the carrier concentration at this time In this case, a sufficient carrier confinement effect could not be obtained.

Therefore, the technical object of the present invention is to improve the confinement of carriers in the active layer by the p-type cladding layer, and to improve the temperature-dependent characteristics such as the maximum oscillation temperature of a semiconductor laser.

[0015]

[Means for Solving the Problems] The present invention provides an oscillation layer including an n-type cladding layer, an active layer, and a p-type cladding layer, each of which is made of an AlGaInP-based compound semiconductor, on the main surface of an n-type semiconductor substrate. 1 lamination step, a second lamination step of forming an n-type block layer on the oscillation layer, and a third lamination step of forming a p-type cap layer on the block layer, After the lamination step and the third lamination step, the method is characterized by comprising a heat treatment step of heat-treating the obtained laminated substrates, respectively.

[0016]

According to the method of the present invention, the overall carrier concentration of the p-type cladding layer can be further increased by performing the heat treatment process twice.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention will be described with reference to FIGS. 2 to 8. The structure of the semiconductor laser manufactured in this example is the same as that in FIG. 1, so the same parts are given the same numbers and the explanation will be omitted.

FIG. 2 shows the first step. In such a process,
A buffer layer (2), an n-type cladding layer (3), an active layer (4), a p-type Cladding layer (5)
, the contact layer (6), and the protective layer (12) in a low pressure MOC.
The layers are sequentially laminated using the VD method. The composition, layer thickness, and dopant of each layer are as shown in Table 1.

[0019]

[Table 1]

[0020] Here, the protective layer (12) is made of p-type GaAs like the cap layer (9) to be formed later on, and is integrated with the cap layer (9) after the cap layer (9) is formed. Therefore, it is omitted in FIG.

FIG. 3 shows the second step. In such a process,
The laminated substrate obtained in the first step is transferred into a heating device (14) equipped with a heater (13), and heat-treated at 520° C. for 10 minutes in an atmosphere of N2/H2=9/1.

At this time, the laminated substrate is placed on a GaAs base (14) placed in the heating device (14) with its laminated surface facing down.
15) Place it on top. This is to prevent As from evaporating from the protective layer (12) on the laminated side surface during the heat treatment.

FIG. 4 shows the third step. In such a process,
On the laminated side surface of the laminate, a thickness of 0.6 μm and a width of 3 to 4 μm is applied.
A striped SiO2 film (16) is provided, and using this as a mask, the protective layer (12) is etched with a sulfuric acid-based etching solution.
47% contact layer (6) and p-type cladding layer (5)
The p-type cladding layer (5) in the etched area is
Etching is performed until the thickness becomes 0.2 μm to form a striped ridge (7). Furthermore, a SiO2 film (1
6), each end portion of 20 μm is removed, and the exposed protective layer (12) is removed using a sulfuric acid-based etching solution.

FIG. 5 shows the fourth step. In such a process,
Using the low pressure MOCVD method, a layer with a thickness of 0.8μ is deposited on the laminated surface.
Block layer (8) made of m Se-doped n-type GaAs
grow. Then, the block layer (8) is selectively laminated only on the exposed p-type cladding layer (5) and contact layer (6) using the remaining SiO2 film (16) as a mask. After that, the exposed SiO2 film (16
) is removed with HF solution.

FIG. 6 shows the fifth step. In such a process,
Using a low pressure MOCVD method, a Zn-doped p layer with a thickness of 2 to 3 μm is deposited on the exposed protective layer (12) and block layer (8).
A cap layer (9) made of type GaAs is laminated.

FIG. 7 shows the sixth step. In such a process,
The laminated substrate obtained in the fifth step is heated again by the heating device (14)
In an atmosphere of N2/H2 = 9/1, heat at 550°C.
, heat treatment for 10 minutes. At this time as well, the laminated substrate is placed on the GaAs base (15) placed in the heating device (14) with its laminated surface facing down.

FIG. 8 shows the seventh step. In such a process,
A p-side electrode (10) in which Cr and Au are sequentially deposited on the cap layer (9), and Cr and S on the other main surface (1b) of the substrate (1).
A semiconductor laser with an oscillation wavelength of 635 nm is manufactured by forming n-side electrodes (11) in which n and Au are sequentially deposited.

Various element characteristics of this embodiment device were investigated. The results are shown in Table 2. For comparison, a comparison device 1 was fabricated by omitting the second and sixth heat treatment steps in the method of fabricating the device of this example, a comparison device 2 was fabricated by omitting only the sixth heat treatment step, and a comparison device 2 was fabricated by omitting only the sixth heat treatment step. Comparative device 3, which was manufactured by omitting only the heat treatment step 2, was also examined for element characteristics in the same manner. The results are also listed in Table 2.

[0029]

[Table 2]

Here, the oscillation threshold value indicates the value when the ambient temperature is 20° C., and the maximum oscillation temperature and maximum optical output indicate the maximum ambient temperature and output values at which continuous oscillation can be performed, respectively. Further, the characteristic temperature indicates the temperature dependence of the oscillation threshold below 30° C., and the larger the value, the less the temperature dependence and the better the oscillation stability.

From Table 2, it can be seen that the device of this embodiment is superior to the comparative device in each element characteristic. The reason for this will be explained below.

First, after various heat treatments were performed by varying the heat treatment temperature in the second step, the carrier concentration of the p-type cladding layer (5) was investigated. The results are shown in FIG.

[0033] The carrier concentration before heat treatment is 7×1017c.
m-3, and it can be seen that the carrier concentration is increased by the heat treatment. This is the p-type cladding layer (5)
This is because the activation rate of Zn added therein increased. In particular, when the heat treatment temperature is 450 to 650°C, 1.6 to 2
．． A high carrier concentration of 0 x 1018 cm-3 was obtained,
When the Zn concentration in the p-type cladding layer (5) at this time was examined, it was found that the activation rate was approximately 100%.

Next, after the fifth step, when the carrier concentration of the p-type cladding layer (5) was examined, it was found that the block layer (8
) was formed, but no change in carrier concentration was observed in the p-type cladding layer (5) directly under the ridge (7) where the block layer (8) was not formed, that is, the p-type cladding layer (7) directly under the ridge (7) excluding the end face. A decrease in carrier concentration was observed in the mold cladding layer (5).

Furthermore, when the carrier concentration of the p-type cladding layer (5) is examined after the sixth step, it is found that the carrier concentration changes in the p-type cladding layer (5) immediately below where the block layer (8) is formed. was not observed, and it was found that after the fifth step, the carrier concentration in the part where the block layer (8) was not formed, where a decrease in carrier concentration was observed, had recovered to the value after the second step. .

Further, when the carrier concentration of the p-type cladding layer (5) of the comparative device 3 in which only the second step was omitted was investigated, it was found that the portion where the block layer (8) is not formed, that is, the ridge (excluding the end face) 7), an activation rate of approximately 100% was obtained in the p-type cladding layer (5) directly under the block layer (8), but in the p-type cladding layer (5) directly under the block layer (8), carriers before heat treatment Only the concentration was obtained.

The reason why these phenomena occur is not known in detail, but considering the above phenomena, in the device of this embodiment, a high carrier concentration is obtained throughout the p-type cladding layer (5); In the comparative device, there are parts where the carrier concentration is low in whole or in part, so it is thought that carriers cannot be sufficiently confined, and the device characteristics at high temperatures or high outputs deteriorate.

Furthermore, in this example, the growth surface of the substrate (1) used was a plane inclined by 5 degrees in the [011] direction from the (100) plane; This is because by using a plane inclined by 5 degrees to the growth plane, the amount of acceptor added to the p-type cladding layer (5) increases, and when this is activated, a higher carrier concentration can be obtained. .

The effect of the method of the present invention is not limited to Zn used as an acceptor in this example, but also to Mg, as shown in FIG. From 2
The height can be increased to x1018 cm-3. However, the temperature of such heat treatment is preferably as low as possible so that the acceptors in the p-type cladding layer (5) do not diffuse into the active layer (4) during the heat treatment, and specifically, the temperature is 550° C. or lower. is preferable.

Further, in this example, a semiconductor laser in which a current non-injection region is provided near the end face of the laser resonator is shown, but of course, a semiconductor laser in which current is injected also near the end face can be used in the same manner as in this example. effect can be obtained.

[0041]

According to the method of the present invention, a first oscillation layer including an n-type cladding layer, an active layer, and a p-type cladding layer each made of an AlGaInP-based compound semiconductor is formed on the main surface of an n-type semiconductor substrate. a second lamination step of forming an n-type block layer on the oscillation layer, and a third lamination step of forming a p-type cap layer on the block layer. After the first lamination step and the third lamination step, the carrier concentration of the p-type cladding layer can be further increased overall by performing a heat treatment step of heat-treating the obtained laminated substrates, respectively. Therefore, the barrier difference between the active layer and the p-type cladding layer can be increased, and the temperature dependence characteristics of the semiconductor laser can be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective cross-sectional view showing an example of an AlGaInP semiconductor laser.

FIG. 2 is a sectional view showing the first step in an embodiment of the method of the present invention.

FIG. 3 is a schematic diagram showing the second step in one embodiment of the method of the present invention.

FIG. 4 is a perspective view showing the third step in one embodiment of the method of the present invention.

FIG. 5 is a perspective view showing the fourth step in an embodiment of the method of the present invention.

FIG. 6 is a perspective view showing the fifth step in an embodiment of the method of the present invention.

FIG. 7 is a schematic diagram showing the sixth step in an embodiment of the method of the present invention.

FIG. 8 is a perspective view showing a seventh step in an embodiment of the method of the present invention.

FIG. 9 is a characteristic diagram showing the carrier concentration of the p-type cladding layer obtained with respect to the heat treatment temperature when Zn is used as an acceptor.

FIG. 10 is a characteristic diagram showing the carrier concentration of the p-type cladding layer obtained with respect to the heat treatment temperature when Mg is used as an acceptor.

Claims (1)

[Claims] Claim 1: On the main surface of an n-type semiconductor substrate, Al
A first lamination step of forming an oscillation layer including an n-type cladding layer, an active layer, and a p-type cladding layer made of a GaInP-based compound semiconductor, and a second lamination step of forming an n-type block layer on the oscillation layer. and a third lamination step of forming a p-type cap layer on the block layer, and a heat treatment step of heat-treating the obtained laminated substrates after the first lamination step and the third lamination step, respectively. A method for manufacturing a semiconductor laser, comprising: