Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – On insulating substrate or layer
Reexamination Certificate
1999-03-24
2001-05-29
Lee, Eddie C. (Department: 2815)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
On insulating substrate or layer
C438S686000, C438S046000, C438S105000
Reexamination Certificate
active
06239005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a metal-semiconductor layered structure provided on an electrically insulating substrate, and also relates to a light emitting semiconductor device including such a layered structure.
2. Description of the Related Art
Heretofore, there has been earnestly required to develop a practically usable blue light emitting semiconductor laser formed by a basic material of gallium nitride (GaN).
FIG. 1
is a schematic view showing a known semiconductor laser formed by a basic material of gallium nitride. It is impossible or practically difficult to obtain a single crystal wafer of gallium nitride, and therefore use is made of a sapphire substrate
1
, and a thin buffer layer
2
of gallium nitride
2
is formed on the sapphire substrate
1
, a first cladding layer
3
formed by a thick n-type gallium nitride layer having a thickness of about 3 &mgr;m is deposited on the buffer layer
2
, an active layer
4
is formed on the first cladding layer
3
, a second p-type cladding layer
5
is formed on the active layer
4
, and a p-electrode
6
is formed on the second cladding layer
5
. A part of a corner of such an assembly is removed by a suitable patterning treatment to expose a part of the first cladding layer
3
, and an n-electrode
7
is formed on the thus exposed surface of the first cladding layer.
In such a known semiconductor laser, a current path is formed from the n-electrode
7
to the p-electrode
6
via the first cladding layer
3
, active layer
4
and second cladding layer. In the known semiconductor laser, since the n-electrode
7
is provided on the exposed surface of the corner portion of the first cladding layer
3
, carriers introduced from the n-electrode travel laterally along the exposed surface and then arrive at the active layer
4
. Therefore, the carrier travelling path becomes longer and has a relatively high electric resistance, and thus a substantial amount of electric power is consumed therein. This also causes an increase in an operating voltage.
Moreover, in order to provide the n-electrode
7
, the assembly of the first and second cladding layers
3
and
5
and active layer
4
has to be partially removed by any suitable patterning process and the manufacturing process is liable to be complicated and through-put is decreased.
The above mentioned problems of the known semiconductor laser could be completely removed if a metal layer serving as an electrode is first formed on an insulating substrate and then a single crystal semiconductor layer is formed directly on the metal layer. In such a structure, carriers introduced from the electrode could be efficiently supplied to the active layer through a thin cladding layer, and therefore an electric resistance of the carrier travelling path could be materially lowered.
Not only the above mentioned semiconductor laser, but also in solar cell and photo-detector, the above structure of the substrate-metal layer-semiconductor layer has been widely used, and thus if the single crystal semiconductor layer could be formed directly on the metal layer formed on the insulating substrate, an efficiency of the device and manufacturing process could be improved to a great extent.
However, it has not been proposed any practical method of forming a semiconductor layer directly on a metal layer formed on an electrically insulating substrate.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a novel and useful method of forming a single crystal semiconductor layer directly or via a very thin buffer layer on a metal layer formed on an electrically insulating substrate.
It is another object of the invention to provide a light emitting semiconductor device, in which a power consumption can be reduced and an operating voltage can be lowered.
According to the invention, a method of forming a single crystal semiconductor layer on a metal layer comprises the steps of:
preparing an electrically insulating substrate having a single crystal structure;
forming an epitaxially grown metal layer on a surface of said electrically insulating substrate; and
forming an epitaxially grown semiconductor layer by epitaxial growth on a surface of said metal layer.
The inventors have conducted various experiments and analyses about the metal-semiconductor structure, and have found that when a metal layer is deposited in a direction of a given crystallographic axis on a predetermined crystal surface of an electrically insulating substrate having a single crystal structure, it is possible to obtain an epitaxially grown metal layer, i.e. a single crystal metal layer. Therefore, by epitaxially growing a semiconductor layer on such an epitaxially grown metal layer, it is also possible to obtain a single crystal semiconductor layer. The present invention is based on such a recognition resulted from the experiments and analysis. That is to say, according to the invention, on a single crystal substrate is formed an epitaxially grown metal layer, and then a single crystal semiconductor layer is epitaxially grown on such a metal layer. In this manner, according to the invention, the single crystal semiconductor layer can be directly formed on the metal layer. Therefore, in a semiconductor device, a metal electrode layer is formed on the substrate, and then a single crystal semiconductor layer is directly or via a buffer layer formed on the metal electrode layer. In this manner, according to the invention, a semiconductor device including the metal-semiconductor layered structure can be manufactured in an efficient manner. That is to say, according to the invention, a single crystal semiconductor layer can be grown directly or via a buffer layer on a metal layer constituting an electrode, and therefore the present invention can be particularly advantageously applied to the manufacture of a semiconductor device formed by a basic material such as gallium nitride which could not be obtained in the form of a wafer. It should be noted that the method according to the present invention could be applied not only to the light emitting semiconductor device such as semiconductor laser and light emitting diode, but also to other kinds of semiconductor devices including the metal-semiconductor layered structure such as solar cell and photo-detector. Furthermore, according to the invention, the semiconductor layer may be epitaxially grown by various kinds of epitaxially growing methods such as metalorganic vapor phase epitaxy (MOVPE), liquid-phase epitaxy (LPE), chemical vapor deposition (CVD) and molecular beam epitaxy (MOE).
In a preferable embodiment of the method of forming an epitaxially grown semiconductor layer on a metal layer according to the invention, an electrically insulating substrate is formed by a sapphire substrate, a platinum (Pt) layer is epitaxially grown on a c-face (0001) of the sapphire substrate in a direction of crystal orientation of (111), a semiconductor layer made of a nitride of III-group semiconductor material is formed on the platinum layer by the epitaxial growth. The inventors have conducted various experiments using sapphire substrates and have found that by depositing a platinum layer in the crystal orientation (111) on the c-face of the sapphire substrate by means of sputtering, it is possible to form an epitaxially grown metal layer, i.e. single crystal platinum layer having a uniform crystal orientation. A reason of such a phenomenon will be considered as follows. Since the thickness of a layer deposited during the sputtering process can be easily controlled, atoms or molecules of platinum can be deposited at a relatively slow rate by finding stable sites of the sapphire substrate or platinum layer. From this view point, according to the invention, the metal layer may be formed by other depositing method such as a liquid-phase epitaxial growth method in which the epitaxial deposition is performed in a much more equilibrium and thermally stable manner. Based on such a recognition, in a preferable embod
Fuke Shunro
Sumiya Masatomo
Yoshimoto Mamoru
Lee Eddie C.
Richards N. Drew
Shizuoka University
Stevens Davis Miller & Mosher LLP
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