Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
1999-06-29
2001-09-18
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C257S094000
Reexamination Certificate
active
06291257
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor photonic devices and a method for forming a ZnO film. More particularly, the invention relates to semiconductor photonic devices using Group III-V compounds such as GaN, InGaN, GaAlN and InGaAlN. The invention also relates to a method for forming a ZnO film deposited on a substrate such as an Si substrate or a glass substrate.
2. Description of the Related Art
As materials for semiconductor photonic devices such as light emitting diodes (LEDs) and laser diodes (LDs) which emit blue light or ultraviolet light, III-V semiconductor compounds represented by the general formula In
x
Ga
y
Al
z
N (where x+y+z=1, 0≦x≦1, 0≦y≦1 and 0≦z≦1) are known. The semiconductor compounds have high light emission efficiency because they are of the direct gap type, and emission wavelengths can be controlled by the In content, and thus these semiconductor compounds have been receiving attention as materials for light emitting devices.
Since it is difficult to form a large single crystal of the In
x
Ga
y
Al
z
N, a so-called “hetero-epitaxial growth method” is used in which a crystal film is grown on a substrate of a different material, and generally it is grown on a c-plane sapphire substrate. However, c-plane sapphire substrates are expensive, and moreover, because of large lattice mismatching, many crystal defects at defect densities of 10
8
/cm
2
to 10
11
/cm
2
occur in the grown crystals, and thus it is not possible to obtain quality crystal films having excellent crystallinity, which is a problem.
In order to reduce lattice mismatching when In
x
Ga
y
Al
z
N is grown on a c-plane sapphire substrate and to obtain crystals having few defects, a method has been developed in which a polycrystalline or amorphous AlN buffer layer or a low pressure growth GaN buffer layer is provided on the c-plane sapphire substrate. In accordance with this method, since lattice mismatching between the c-plane sapphire substrate and the buffer layer is reduced and at the same time lattice mismatching between the buffer layer and In
x
Ga
y
Al
z
N is reduced, a crystal film having few defects can be obtained. However, in addition to the expensive c-plane sapphire substrate in this method, the structure becomes complex, resulting in a further increase in cost.
Additionally, an SiC substrate has been investigated, and there is small lattice mismatching with the SiC substrate. However, SiC substrates are much more expensive in comparison with c-plane sapphire substrates (approximately 10 times as costly as c-plane substrates), which is disadvantageous.
Accordingly, it has been conventionally desired that semiconductor photonic devices be fabricated using inexpensive Si substrates or glass substrates. For that purpose, an In
x
Ga
y
Al
z
N-based light emitting device may be constructed by depositing a ZnO film (buffer layer) having a hexagonal system oriented in the c-axis direction on an Si substrate or glass substrate and by forming a semiconductor containing GaN thereon.
When a ZnO buffer layer is provided on an Si substrate, the substrate cost can be limited to approximately one-tenth of that of a c-plane sapphire substrate, enabling low cost. Additionally, while a c-plane sapphire substrate is an insulating material, an Si substrate can be made conductive and a p-type electrode and an n-type electrode can be provided on the upper side and the lower side of the light emitting device, thus simplifying the structure of the device.
In the past, it was not possible, simply by forming a ZnO film oriented in the c-axis direction on an Si substrate, to grow a thin film containing GaN having good crystallinity thereon. Since the c-axis orientation of the ZnO film sensitively affects the crystallinity of the thin film containing GaN formed thereon, in order to form a thin film containing satisfactory GaN thereon, a ZnO film having the best possible c-axis orientation must be obtained.
SUMMARY OF THE INVENTION
The present invention is directed to a semiconductor photonic device that can solve the technical problems described above, and it is an object of the present invention to form a Zno film (ZnO buffer layer) having satisfactory c-axis orientation on a substrate so that a semiconductor layer containing satisfactory GaN can be grown thereon.
In a method for forming a ZnO film in accordance with the present invention, a ZnO film oriented in the c-axis direction is formed on a substrate, and by setting the film thickness at about 3,500 Å or more, a ZnO film having satisfactory rocking curve characteristics can be obtained.
In the present invention, in a semiconductor photonic device using a compound semiconductor represented by In
x
Ga
y
Al
z
N (where x+y+z=1, 0≦x≦1, 0≦y≦1, and 0≦z≦1), a ZnO buffer layer having satisfactory rocking curve characteristics is formed on a substrate by orienting a ZnO buffer layer having a thickness of about 3,500 Å or more in the c-axis direction, and a semiconductor layer containing GaN is formed on the ZnO buffer layer.
In accordance with the present invention, since the rocking curve half-width of the ZnO buffer layer oriented in the c-axis direction can be set at 4.5° or less, satisfactory c-axis orientation can be achieved and the semiconductor layer formed on the ZnO buffer layer can have satisfactory crystallinity.
More preferably, the thickness of the ZnO buffer layer is increased so that the ZnO buffer layer has a rocking curve half-width of 3.5° or less, and in particular, the rocking curve half-width is desirably set at 2.5° or less.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
REFERENCES:
patent: 5670798 (1997-09-01), Schetzina
patent: 19629720 A1 (1997-02-01), None
Patent Abstracts of Japan; Publication No.10178202A; Published 6/30/98.
Christianson Keith
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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