Stock material or miscellaneous articles – Sheet – web – or layer weakened to permit separation through...
Reexamination Certificate
1998-08-28
2001-04-10
Kunemund, Robert (Department: 1765)
Stock material or miscellaneous articles
Sheet, web, or layer weakened to permit separation through...
C117S004000, C117S007000, C117S950000, C438S460000
Reexamination Certificate
active
06214427
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates generally to electronic devices such as light emitting diodes (LEDs), and more particularly to a method of making an electronic device having a single crystal substrate formed from a polycrystalline material.
2. Description of the Related Art
LEDs, laser diodes, and other electronic devices are typically manufactured by depositing various layers of semiconductor materials on a substrate. A know group of semiconductor materials which is useful in forming light-emitting devices is the gallium nitride (GaN) system. The gallium nitride system refers to semiconductor materials comprising one or more of the group III nitrides, GaN, AIN, and InN. The GaN system allows various wavelengths of light, particularly the shorter wavelengths, to be produced based on the relative amounts of GaN, AIN, and InN in the composition.
Gallium nitride-based semiconductor devices are commonly formed on a substrate comprising sapphire, a single crystal alumina (Al
2
O
3
). Typically, the sapphire substrate is produced by growing a single alumina crystal from molten alumina, and subsequently cutting the sapphire body in the shape of a thin wafer. However, the process of growing a sapphire crystal from a melt is relatively expensive due to the need to carefully control the growing conditions. In addition, the resulting crystal typically must be cut with a diamond saw, ground, and polished into the shape of a wafer. In addition to being expensive, this process limits the types of shapes which can be produced.
It would be desirable, therefore, to have a process for forming a sapphire substrate which decreased the amount of cutting, grinding and polishing required, thereby decreasing the cost of the substrate, and which could be used to form substrates of a variety of shapes useful for different electronic devices.
SUMMARY
A method of making an electronic device, according to an exemplary embodiment of the invention, comprises the steps of: forming a polycrystalline substrate in a desired shape; converting the polycrystalline substrate into a single crystal substrate using a solid state crystal conversion process; and forming an electronic element on the substrate.
According to a preferred embodiment, alumina is formed in the shape of a wafer, sintered to form a densified polycrystalline alumina wafer, and heated to a temperature between the melting point of alumina and one-half the melting point of alumina to convert the densified polycrystalline alumina wafer into a sapphire wafer. A light-emitting diode or other electronic device, such as a laser diode, a high frequency microwave device, or an optoelectronic detector, can be formed on the wafer by depositing layers of semiconductor material on the wafer.
The method provides several advantages in forming electronic devices. For example, the cost of the single crystal substrate is significantly reduced since crystal growing from a melt is unnecessary. Also, less processing is required after the crystal is formed, since the precursor polycrystalline substrate can be formed to near net shape. In addition, the polycrystalline substrate can be formed into many shapes, in contrast to the limited shapes possible when growing a crystal from a melt.
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Champagne Donald L
General Electric Company
Johnson Noreen C.
Kunemund Robert
Vo Toan B.
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