Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
1997-11-26
2001-07-10
Nguyen, Tuan H. (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S047000, C438S796000
Reexamination Certificate
active
06258614
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a semiconductor device that can be used as a light-emitting device and to a method of manufacturing such device. In particular, the invention relates to a semiconductor light-emitting device and its manufacturing method, where the confinement structure and low resistance areas are easily formed, the reproducibility thereof is superior, and the yield thereof is very high.
2. Description of the Prior Art
As shown on
FIG. 1
, a semiconductor laser having a layered structure is formed from a substrate
70
, n-type cladding layer
71
, active layer
72
, and p-type cladding layer
73
. A top electrode
74
and a bottom electrode
75
are placed at the two ends of this layered structure.
When current is injected into the active layer
72
from the top electrode
74
, light resonance arises in the active layer
72
and laser light
76
is emitted in a prescribed direction, e.g. in a perpendicular direction for vertical cavity surface emitting lasers. Because current is supplied to the active layer
72
from the top electrode
74
, the p-type cladding layer
73
must have a low resistivity (generally, about 1&OHgr;·cm). Japanese Unexamined Patent Publication No. 5-183189 disclosed a technology that may be used to make a low resistivity p-type cladding layer
73
.
In the semiconductor laser device having the form shown on
FIG. 1
, the p-type cladding layer
73
extends over the entire structure and has uniform resistivity. Accordingly, the following problems arise:
Light emission efficiency decreases;
Threshold current at the start of oscillation becomes large;
The device is easily destroyed by the generation of heat; and
During oscillation operation the device becomes unstable.
A known solution to the above problems is to use a conventional current-confined semiconductor laser device, as shown in FIGS.
2
(A) to
2
(C). The laser device in FIG.
2
(A) has a planar stripe structure in which an n-type contact layer is formed on a p-type cladding layer; and in which a top electrode is formed after Zn that is diffused in a striped form reaches the p-type cladding layer through the n-type contact layer. The structure is referred to as a confinement type structure, although the current spread in such device is large and the degree of confinement is poor.
The laser device shown on FIG.
2
(B) has a proton implanted structure. In this device, a p-type contact layer is formed on a p-type cladding layer. The top electrode is formed in a striped part that remains after protons are implanted. To make this structure, it is necessary to control the amount of implantation of the protons. Because this process exhibits inferior reproducibility, it is not easy to use the process to fabricate devices of uniform quality.
The laser device shown on FIG.
2
(C) has a buried heterostripe structure and, as such, it is layered with an n-type cladding layer, an active layer, a p-type cladding layer on an n-type substrate (InP), a top electrode, and a bottom electrode. This structure exhibits excellent current confinement because the p-type cladding layer has a confinement structure. However, in forming the confinement structure, manufacturing becomes complex because etching and regrowth are essential steps.
For laser devices, such as those shown on FIGS.
2
(A) to
2
(C), where the laser device has a current-confined structure, processing cannot usually be repeated when a processing error occurs. Therefore, such processes as are used to produce these devices result in poor yields and an accompanying negative effect on manufacturing costs.
Except for the structure of FIG.
2
(C), generally, when a structure that confines the current in the light emitting area is formed in a laser device, the bonding area between the contact layer and electrode layer necessarily becomes narrow. As a result, the contact resistance between the semiconductor and metal becomes large, Joule heat arises in the contact while the element is operating, and the characteristics of the element deteriorate.
An annealing method that consists of heating by a heater and electron beam radiation, in addition to laser light radiation, produces problems related to local heating when the device is heated by the heater. Consequently, a method other than local heating must be devised to form the current-confinement structure. For electron beam radiation, local heating is possible. However, because the electron beam scans, annealing by this technique takes considerable time and therefore significantly reduces process productivity.
SUMMARY OF THE INVENTION
The invention provides a semiconductor device, in particular a light-emitting semiconductor device, e.g. a semiconductor laser device, or a semiconductor LED device, and a method for manufacturing same. The device has superior current confinement, is easily manufactured, has superior reproducibility, and has improved yield, as well as allowing ample degrees of freedom in designing the confinement.
The manufacturing method herein described includes a step that irradiates the light-emitting device with laser light at a wavelength that is absorbed in the semiconductor layer in a part of, or the entire, semiconductor layer, such that the resistivity of the semiconductor layer is changed by annealing produced by said laser light in said irradiated zone. The exemplary embodiment of the invention provides a p-type semiconductor, although the same laser annealing step can be implemented for an n-type semiconductor.
In the invention, such annealing is accomplished by using laser light irradiation (hereinafter called laser annealing) to decrease or increase the resistance in a part of, or the entire area of, the p-type semiconductor layer. If laser annealing is performed under specific conditions, i.e. in an atmosphere of N
2
, in a part of or the entire area of the p-type semiconductor layer where the activation coefficient of the acceptor impurities is low (that is, for high resistance), the area can attain a low resistance. In contrast, if laser annealing is performed under specific conditions, i.e. in an atmosphere of NH
3
, in a part of or the entire area of the p-type semiconductor layer where the activation coefficient of the acceptor impurities is high (that is, for low resistance), the area can attain a high resistance.
The manufacturing method applies to a p-type semiconductor layer that is formed by a single crystal growth process having a resistivity that is changed by annealing. According to this method, a semiconductor device is fabricated in which the semiconductor layer includes a low resistance zone where the activation coefficient of the acceptor impurities is high, and a high resistance zone where the activation coefficient of the acceptor impurities is low.
When the herein described manufacturing method is used, a light-emitting device, e.g. laser device or LED device (including the surface emitting type), can be manufactured with or without stripes. In addition, the invention can be used to manufacture a variety of layered structures, such as double hetero structures or single hetero structures. For example, if a double heterostructure is adopted, the n-type cladding layer, active layer, and p-type cladding layer are layered in this or the opposite order. Laser annealing can be used in such structures to create a low resistance region, where the activation coefficient of the acceptor impurities is high, and a high resistance region, where the activation coefficient of the acceptor impurities is low, in parts of the p-type cladding layer.
Furthermore, when the herein described manufacturing method is used, a p-type semiconductor layer can be easily manufactured, where the low resistance region provides confinement. Thus, a confinement type, low resistance region can be formed by laser annealing to give a part of the p-type semiconductor layer either low or high resistance.
In the former case, laser light at a wavelength that is absorbed into the high resistance p-type semiconductor is converged or diverged by a lens or
Leiterman Rachel V.
LumiLeds Lighting U.S., LLC
Nguyen Tuan H.
Ogonowsky Brian D.
Skjerven Morrill & MacPherson LLP
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