JPH03276687A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To change-over gradually group V gas in a third layer and to suppress the generation of a crystal defect in each growth layer to be formed after the group V gas is changed-over by a method wherein the third layer, which is constituted of group V elements of As and P, is provided between a first layer, which is constituted of a group V element of As, and a second layer which is constituted of a group V element of P. CONSTITUTION:A first buffer layer 2 consisting of an N-type GaAs, a second buffer layer 3 consisting of an N-type Ga1-xInxAsyP1-y, a third buffer layer 4 consisting of an N-type Ga0.48In0.52P, an N-type clad layer 5 consisting of an N-type AlGaInP, an active layer 6 consisting of an undoped GaInP, a P-type clad layer 7 consisting of a P-type AlGaInP, a contact layer 8 consisting of a P-type GaInP and a cap layer 9 consisting of a P-type GaAs are epitaxially grown continuously and in that order on one main surface of a substrate 1. At this time, the layer 3 is changed its composition from the side of the layer 2 by changing gradually the amount of supply of each raw gas and is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a semiconductor laser whose oscillation layer is made of an AlGaInP-based compound semiconductor.

(b) Prior art AlGaInP has a wavelength in the 0.6 μm band and is used as a visible light semiconductor laser.

FIG. 5 shows a conventional AlGaInP semiconductor laser, which is described in, for example, Japanese Patent Laid-Open No. 62-200786.

In the figure, (20) is a substrate made of n-type GaAs;
(21) is an n-type GaAs buffer layer, (22) is an n-type G
aInP buffer layer, (23) is n-type cladding layer made of n-type AIGaInP, (24) is undoped GaI
The active layer (25) is made of nP and the p-type cladding layer is made of p-type AlGa1nP. These layers are the well-known MO
Epitaxial growth is sequentially performed on the -main surface of the substrate (20) using the CVD method. Furthermore, a striped ridge (26) with a diameter of about 5 μm is formed in the p-type cladding layer (25) by etching.

(27) is the p-type cladding layer (excluding the top of the ridge (26)
25) A block layer made of n-type GaAs formed on the top, and (28) a block layer formed on the exposed top of the ridge (26) of the p-type cladding layer (25) and on the block layer (27).
A cap layer made of type GaAs, (29) is a p-side electrode formed on the cap layer (28), and (30) is a substrate (2).
0) is an n-side electrode formed on the other main surface.

(c) Problems to be Solved by the Invention In such a conventional apparatus, when epitaxially growing an n-type GaInP buffer layer on an n-type GaAs buffer layer, the raw material gas of group V gas must be switched from As to P. Must be.

However, it is difficult to instantly replace the As supply gas and the P supply gas when switching between group V gases. Therefore, immediately after switching, As is also incorporated into the growth layer, which causes Ga1nP, which is normally lattice matched to GaAs, to be incorporated into the growth layer.
Since the lattice constant of the crystal changes, lattice mismatch occurs and crystal defects are more likely to occur in the grown layer. Furthermore, since the crystallinity of the layer formed on the grown layer with crystal defects deteriorates, there is a problem that the manufactured semiconductor laser itself has poor characteristics and is easily deteriorated.

Furthermore, even when forming a GaInP layer directly on a GaAs substrate, in order to suppress As having a high vapor pressure from escaping from the substrate when the substrate is heated to the growth temperature, it is necessary to
s must be supplied, and the group V gas must be switched as well.

Therefore, the present invention provides a semiconductor laser made of AlGa1nP yarn, in which crystal defects are less likely to occur at the interface even when the group V gas is switched, and the grown layer has good crystallinity after the gas is switched.

(d) Means for Solving the Problems The present invention provides a semiconductor laser in which the oscillation layer including the active layer is made of an AIGaInP-based compound semiconductor, and in order to solve the above problems, the group , between the first layer made of As and the second layer made of P, the group V elements constituting the layer are composed of As and P, and the composition ratio is set so as to lattice match with the first layer. It is characterized by comprising a third layer.

(E) Effect According to the present invention, between the first layer in which the group V elements constituting the layer are As and the second layer in which the group V elements constituting the layer are P, the group V elements constituting the layer are composed of As and P. By providing a third layer whose composition ratio is set to lattice match with the first layer, the lattice constant at each layer interface is kept constant.

(F) Embodiment FIG. 1 shows an embodiment of the present invention. In the figure, (1)
is a substrate made of n-type GaAs. (2) is 0.3μ
a first buffer layer made of n-type GaAs with a thickness of m, (3)
is a 1 μm thick n-type Ga+ −*I nx A s
yP, the second buffer layer consisting of □, (4) is 0.3 μm
The third buffer layer consists of n-type Ga (<s I n++1*P, (5) is 0.8 μm thick n-type AIGa
An n-type cladding layer made of InP, (6) an active layer made of undoped GaInP with a thickness of 0.1 μm, and (7) a 0.1 μm thick active layer made of undoped GaInP.
．． A p-type rad layer made of p-type AIGaInP with a thickness of 8 μm, (8) a contact layer made of p-type Ga1nP with a thickness of 0.1 μm, and (9) a p-type Ga with a thickness of 0.4 μm
The cap layer is made of As, and these layers are successively epitaxially grown on the -main surface of the substrate (1).

At this time, the second buffer layer (3) is gradually changed from the first buffer layer (2) side to X from O to 0.52, y from 1 to 0, and y from 1 to 0. As shown by the broken line in Figure 2, while satisfying the value of X + V,
It is formed by changing the composition.

Here, the broken line in Fig. 2 indicates GaAs, Gap-, InxA
s and Pl-7 are lattice matched.

In addition, a p-type rad layer (7), a p-type contact layer (8)
, the cap layer (9) has p
The patterned rad layer (7) is selectively etched until the thickness becomes 0.2 μm, thereby forming the p-type rad layer (7).
) is provided with a ridge (10).

(11) is an insulating layer made of Sin deposited on the exposed p-type rad layer (7) and on the side surfaces of the ridge (10);
12) includes the exposed top of the ridge (10) and the insulating layer (11).
), and (13) is an n-side electrode formed on the other main surface of the substrate (1).

In the manufacturing process of this embodiment, the p-type rad layer (7)
After epitaxial growth, we observed the surface state,
The number of crystal defects called hillocks was measured at 20.
It was less than 0 pieces/cm'.

For comparison, we measured the number of crystal defects on the p-type rad layer of a comparative device manufactured in the same manner as the device of this example except that the second buffer layer (3) was not provided, and found that it was approximately 8000. pieces/cm”.

Further, 25 units each of the device of this embodiment and the comparative device were manufactured, and their oscillation threshold currents were measured. The measurement results of the device of this embodiment are shown in FIG. 3(a), and the measurement results of the comparative device are shown in FIG. 3(b).

As is clear from the measurement results, it can be seen that the device of this embodiment has small variations in the oscillation threshold current, and that a semiconductor laser with a small oscillation threshold current can be manufactured with a high yield.

FIG. 4 shows another embodiment of the present invention, in which the same parts as in FIG. 1 are given the same numbers and their explanation will be omitted.

In the figure, (14) is the first layer made of n-type AjGaAs.
Buffer layer, (15) is n-type (A'Ga)+-x
I n, A S.

A second buffer layer made of Pl-1 and provided between the substrate (1) and the n-type cladding layer (5). Further, in this embodiment as well, the second buffer layer (15) is formed by gradually changing the supply amount of each raw material gas.
) side, X from 0 to 0.52, y from 1 to 0,
As shown by the broken line in FIG. 2, the composition is changed while satisfying the x and y values.

In this embodiment as well, the number of crystal defects appearing on the surface of the n-type cladding layer (7) is approximately 500/cm'', similar to the structure shown in FIG. 1, and a semiconductor laser with a small oscillation threshold current is A good yield was obtained.

(G) Effects of the Invention According to the present invention, between the first layer in which the V group elements constituting the layers are As and the second layer in which the V group elements constituting the layers are P, the V group elements constituting the layers are As and P. By providing a third layer consisting of The occurrence of crystal defects in each growth layer formed after switching the V group gas is suppressed, and the characteristics are shown in FIG.
As and Gal-++ I nmAsyP l-F, or AtGaAs and (A jGa)+-, InxA
A diagram showing the values of x and y where s and P l-F are lattice matched,
3(a) and 3(b) are characteristic diagrams showing the oscillation threshold currents of the device of this embodiment and the comparative device, respectively, FIG. 4 is a sectional view showing another embodiment of the present invention, and FIG. The figure is a sectional view showing a conventional structure.

Claims (1)

[Claims] (1) In a semiconductor laser in which the oscillation layer including the active layer is made of an AlGaInP-based compound semiconductor, a layer is formed between the first layer in which the group V element constituting the layer is As and the second layer in which P is A semiconductor laser comprising a third layer in which group V elements constituting the layer are As and P, and the composition ratio thereof is set to be lattice matched with the first layer.