JPS6284580A - Manufacture of optical semiconductor device - Google Patents

Abstract

PURPOSE:To flatten the surface of a buried type semiconductor laser, and to inhibit leakage currents by thickly growing a high resistance layer up to the thickness capable of flattening, covering a projecting section in a light-emitting section, introducing an impurity to the high resistance layer on an active layer through a diffusion, an ion implantation, etc. in order to ensure a current injection path to the active layer and lowering a resistance value. CONSTITUTION:An InGaAsP layer 2 as an active layer and a P-InP layer (a clad layer) 3 as a first semiconductor layer are grown on a semiconductor layer 1 formed onto a semiconductor substrate in succession, and these layers on both sides of a light-emitting region and one part of the N-InP substrate 1 are removed, thus shaping a projecting section. A P<->-InP layer (a buried layer) 4 having high resistance is grown so that the surface is flattened, covering said projecting section as a second semiconductor layer. A P-type impurity is introduced to the P<->-InP layer layer 4 just above the active layer 2, thus shaping a P<+> type region 5 so as to reach the P-InP layer 3 from the surface.

Description

[Detailed Description of the Invention] [Summary] Leakage current of a buried semiconductor laser is suppressed by using a high resistance layer, and this layer is grown thickly so that the surface thereof becomes flat, and is diffused into this layer above the active layer. Alternatively, a current injection path to the active layer is secured by impurity introduction means such as ion implantation.

[Industrial application field]

The present invention relates to a method of manufacturing an optical semiconductor device, and more particularly to a method of manufacturing a buried semiconductor laser that effectively utilizes a high resistance layer to reduce leakage current.

A buried semiconductor laser has a structure in which both sides of a convex part made up of an active layer that participates in light emission and upper and lower cladding layers that sandwich this layer and act to confine light are buried with buried layers. In order to improve the threshold current, efficiency, temperature characteristics, etc. of the active layer, it is necessary to effectively inject current into the active layer.
Leakage current that passes through the buried layer without passing through the active layer must be suppressed as much as possible.

[Conventional technology]

FIGS. 2(1) to 2(3) are cross-sectional views of a conventional buried semiconductor laser.

This structure is the main type of buried semiconductor laser.FB)
l(Flat Buried Heterojunct
ion) called a laser.

FIG. 2 (in 11, 1 is a semiconductor base, a semiconductor substrate,
Alternatively, it is a semiconductor layer formed on a semiconductor substrate, such as an n-type indium 1% (n-InP) plate, on which an active layer is made of indium gallium arsenide phosphide (InGaAsP).
) layer 2, p-type indium W (p-In
P) Layers 3 are sequentially grown, these layers on both sides of the light emitting region and a part of the n-1nP substrate 1 are removed to form a convex portion, and then p-1nP layers 6, nP are grown as buried layers. -InP layer? ,
A p-1nP layer 8 is sequentially grown.

In this laser, the forward rising voltage of the heterojunction diode formed by the active layer and the InP layer is lower than that of the InP homojunction diode 9, and the fact that almost no current flows through the reverse junction 10 reduces the spread of leakage current. Preventing.

In order to make this effect effective, as shown in Figure 2 (2), p-1
The carrier concentration of nP H6 is increased to p・-InP, and the n-
The rate of reaching the 1nP layer 7 is reduced.

For this reason, the horizontal spread of leakage current is suppressed,
A small amount of leakage current will flow through the 11 paths.

If p-InP with a low carrier concentration is used as the p-InP layer 6 as shown in FIG. Therefore, an excessive current flows in the current path 12 due to the slight gate current flowing in the path 11 for the cyrisk made of InP M 1.6.7.8. Therefore, the leakage current spreads widely in the lateral direction.

In view of the above, at present, a structure shown in FIG. 2 (2) in which the pdnP layer 6 is made of p''-InP is adopted as a structure for suppressing leakage current.

However, even in this structure, the laser characteristics are not necessarily good. This is considered to be because the leakage current is suppressed only by the magnitude of the rising voltage of the pn junction.

Therefore, attempts are being made to use a high resistance layer as the buried layer.

FIGS. 3(1) and 3(2) are cross-sectional views of a conventional buried semiconductor laser using a high resistance layer as a buried layer.

In FIG. 3(1), high resistance layers (p
--1nP layer) 13 is embedded.

As a result, when a lateral leakage current flows, the high resistance layer 1
Due to the large voltage drop at 3, the homojunction diode 9
This has the effect of suppressing the bias voltage applied to the device to a low level, resulting in a reduction in leakage current.

However, since the above-mentioned electron arrival rate in this high resistance layer 13 is large, it is not possible to provide a reverse junction 10 as shown in FIG. 2.

However, with this structure, the surface is not flat, so
The manufacturing process becomes difficult, and the mounting condition on the heat sink becomes poor, resulting in heat radiation problems.

Therefore, in order to flatten the surface, as shown in Figure 3 (2),
If the p-TnP layer 14 is grown as the top layer in the conventional manner, the leakage current in the lateral direction of the path 15 increases through this layer, resulting in the disadvantage that the effect of the high resistance layer 13 cannot be fully utilized.

[Problem that the invention seeks to solve]

In a buried semiconductor laser, it has been difficult to suppress leakage current and obtain a flat structure.

[Means for solving problems]

The solution to the above problem is to sequentially grow an active layer (2) and a first semiconductor layer (3) of a different conductivity type on a semiconductor base (1) of a negative conductivity type, and to a semiconductor layer (3);
The active layer (2) and a portion of the semiconductor base (1) are removed to form a convex portion, and the first semiconductor layer (
3) Growing a second semiconductor layer (4) with higher specific resistance, and introducing impurities of other conductivity type so that it reaches the first semiconductor layer (3) from the surface of the second semiconductor layer (4). This is achieved by the method for manufacturing an optical semiconductor device according to the present invention, which includes the steps of:

[Effect]

If a high resistance layer is used as a buried layer to prevent leakage current in a buried semiconductor laser, it becomes difficult to flatten the surface. Therefore, in order to grow a high-resistance layer thick enough to cover the convex part of the light-emitting part and flatten it, and to ensure a current injection path to the active layer, ions are diffused and ion-implanted into the high-resistance layer above the active layer. By introducing impurities, etc., the resistance value is lowered. In this way, it is possible to achieve both flattening of the surface and suppression of leakage current.

〔Example〕

FIGS. 1(1) to 1(3) are cross-sectional views of a buried semiconductor laser using a high resistance layer as a buried layer according to the present invention.

In FIG. 1 (1), l is a semiconductor base, a semiconductor substrate,
Alternatively, it is a semiconductor layer formed on a semiconductor substrate, for example an n4nP substrate, and an active layer on which InGaAsP is formed.
Layer 2 and p-InP layer (cladding layer) 3 as the first semiconductor layer are grown in sequence, and these layers and n-
A portion of the InP substrate 1 is removed to form a convex portion.

In FIG. 1(2), a high-resistance p-InP layer (buried layer) 4 is grown as a second semiconductor layer to cover the convex portion and to flatten the surface.

In FIG. 1(3), a p-type impurity is introduced into the p-InP layer 4 directly above the active layer 2, and a ρ° type region 5 is formed so as to reach the p-1nP layer 3 from the surface.

With the above steps, the main steps of the laser are completed, and then the normal steps are performed to form electrodes, cleave the end face of the resonator, mount, etc., and complete the device.

〔Effect of the invention〕

As described in detail above, according to the present invention, the surface of a buried semiconductor laser can be flattened and leakage current can be suppressed.

[Brief explanation of drawings]

Figures 1 (1) to (3) are cross-sectional views of a buried semiconductor laser using a high resistance layer as a buried layer according to the present invention, and Figures 2 (1) to (3).
(3) is a cross-sectional view of a conventional buried semiconductor laser, and FIG. 3 (1) and (2) are cross-sectional views of a conventional buried semiconductor laser using a high-resistance layer as a buried layer. . In the figure, 1 is a semiconductor base, for example, an n-InP substrate; 2 is an active layer, InGaAsP JiL; 3 is a first semiconductor layer, a p-1nP layer (cladding layer);
is the second semiconductor layer, which is the p-InP layer, and 5 is the p-type region (the 1st and a half part of the L-face of the V-V). Figure 9 苧 2 Mouth 1zu a5 Hole 5ri J's L-bupa's γ-plane diagram 03) Dream 3 prisoners

Claims (1)

[Claims] An active layer (2) and a first semiconductor layer (3) of another conductivity type are sequentially grown on a semiconductor base (1) of one conductivity type, and the first semiconductor layer (3) other than the light emitting region is The active layer (2) and a part of the semiconductor base (1) are removed to form a convex portion, and a second semiconductor layer having a resistivity higher than the first semiconductor layer (3) is formed to cover the convex portion. The second semiconductor layer (4) is grown, and the second semiconductor layer (4) is grown.
4) A method for manufacturing an optical semiconductor device, comprising the step of introducing an impurity of another conductivity type so as to reach the first semiconductor layer (3) from the surface.