Method of making a crystalline multilayer structure at two press

Details Method of making a crystalline multilayer structure at two press Method of making a crystalline multilayer structure at two press

1996-02-09

1997-06-10

Bowers, Jr., Charles L.

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

117 93, 117952, H01L 2120

Patent

active

056375310

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process of manufacturing crystalline structure and more specifically to crystalline multilayer structures based on nitrides of group III metals, and manufacturing method thereof.


BACKGROUND OF THE INVENTION

Gallium nitride "GaNt" Aluminum nitride "AlN" and Indium nitride "INN" are known as semiconductor compounds of large direct energy gaps. As such they are important electronic materials.
AlN, in the form of ceramic substrate, is applied in high power electronic applications, because of its high heat conductivity, thermal expansion co-efficient close to that of silicon, and good stability at high temperatures.
It has long been known that among the nitrides of group III metals, GaN has potentially the best useful properties as a semiconductor device. Specifically, GaN has semiconducting properties for temperatures up to 600.degree. C. as compared to silicon semiconductor with temperature stability of up to 120.degree. C. The temperature stability and large energy gap of GaN can provide many new high temperature applications for electronic products.
A second important characteristic is that a GaN p-n Junction light emitting diode ("LED") emits visible blue light with a wavelength of approximately 450 nm. GaN has a high efficiency of radiative recombination, and low dislocation mobility. The other semiconductors which are known to emit light in that band are silicon carbide (SIC) and generally A.sup.II B.sup.VI semiconductors such as ZnSe and CdF.sub.2. However, because it is an indirect bandgap material, the luminous efficiency of SiC is only about 0.04 lumen/watt. The A.sup.II B.sup.VI are known to have high defect mobilities and dislocation densities, which reduce their useful life and the power level at which they can operate. In contrast, it is anticipated that LED's made from GaN would have a luminous efficiency of about 0.6 lumen/watt, and remain extremely stable over time.
Thus-GaN and other group III metal nitrides are viable candidates for applications in short wavelength optoelectronics, blue laser systems, full color display systems and high temperature electronics.
Despite their many advantages, nitrides of group III metals including GaN have not been used extensively because of the many difficulties involved in growing such nitrides in bulk crystals. Their thermodynamic properties preclude the standard techniques for the growth of bulk single crystals, appropriate for commercial use. For instance, the high melting temperature and high N.sub.2 pressure at melting, of GaN is in the range where the compound is unstable and readily dissociates. Due to the high melting temperature, the substrate crystals of GaN cannot be obtained by typical crystal growing methods like Czochralski or Bridgman growth from the stoichiometric melts.
Because of the difficulties to produce substances of pure crystalline nitrides of group III metals, the prior art methods use substrates made of materials other than group III nitrides, to develop crystalline nitrides. For example, the nitrides of group III metals like gallium nitride, aluminum nitride, indium nitride or their alloys are deposited on crystalline substrates of different chemical compositions like sapphire or silicon carbide, by Molecular Beam Epitaxy ("MBE") or Metal Organic Chemical Vapor Deposition ("MOCVD").
Specifically atoms of group III metals like gallium and atoms of nitrogen are deposited on a single crystalline substrate by causing them to collide with the substrate. In such known procedures gallium atoms are provided by vaporizing liquid gallium at 1800.degree. C. Nitrogen atoms ere generated from a flow of molecular nitrogen exposed to plasma causing its molecules to dissociate. It is also possible to apply accelerated positive ions by using an electric field for the acceleration to dissociate the nitrogen molecules.
Another prior art method for developing GaN crystal is known as metal organic chemical vapor deposition. Accordingly, the gallium nitride is deposited on a sapphire substrate, by

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