Chemistry of inorganic compounds – Boron or compound thereof – Binary compound
Patent
1999-06-18
2000-09-19
Langel, Wayne
Chemistry of inorganic compounds
Boron or compound thereof
Binary compound
423409, 423411, 423412, C01B 21064, C01B 2106, C01B 21076, C01B 21072
Patent
active
061207489
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
This invention was made in part with support from the National Science Foundation Grant Number DMR 9315914.
The present invention relates to a process for forming high quality crystalline refractory materials, particularly gallium (Ill) nitride (GaN), from solid precursors. GaN is a material newly available for use in the optoelectronics industry fur the fabrication of light-emitting diodes (LEDs) and blue lasers. It is also possible that doped GaN crystals may have utility as semiconductors. A particularly suitable application is the replacement of standard light bulbs in large outdoor displays, traffic lights and street lighting by GaN LEDs. GaN crystals, when properly activated, fluoresce producing a bright blue glow which is about 60 times brighter than the best GaP based yellow-green LEDs and many times brighter than a standard light bulb which it would replace. Further, a GaN LED display would have an operating life far in excess of the standard light bulb.
Currently, bulk quantities of high purity, polycrystalline gallium nitride are not available. Current techniques to produce such materials require maintaining reactants at high temperatures and pressures for long periods of time. Prior attempts to manufacture GaN by reacting gallium iodide with lithium nitride, which appears to be a suitable approach, produces elemental Ga, nitrogen and Lil and not GaN. Thus there is a need for a low cost, rapid process to produce large quantities of powdered crystalline materials for use in such applications as lighting, signal displays, and flat screen displays for computers and television screens.
SUMMARY
These needs are met by the present invention which comprises a low temperature process for directly forming crystals of refractory nitrides by blending dry reactants in an oxygen and moisture free environment, placing the reactants in a sealed vessel, pressurizing the reactants to in excess of 5 kilobars (5000 atmospheres) and rapidly exposing the reactants to a temperature in excess of about 225.degree. C. The soluble salt by-products are then extracted from the resultant mixture, leaving high purity crystals of the nitride in the form of a fine powder.
The invention can be used for preparing a wide variety of refractory materials. However, it is particularly suitable for preparing gallium nitride (GaN). In a first embodiment Gal.sub.3 is mixed with Li.sub.3 N, the mixture is placed in a pressure vessel and heated by exposure to a resistively heated wire. It was discovered that performing this reaction at pressures in excess of 5 kbar resulted in GaN instead of elemental gallium and nitrogen.
DRAWINGS
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and accompanying drawings, where:
FIG. 1 is a front schematic view of an apparatus used to perform the process embodying features of the invention.
FIG. 2 is an enlarged exploded front schematic view of a first type of reaction chamber used with the apparatus of claim 1.
FIG. 3 is an enlarged exploded front schematic view of a second type of reaction chamber used with the apparatus of claim 1.
FIG. 4 is an X-ray diffraction pattern elicited from the solid products of the solid-state metathesis reaction at ambient conditions of Gal.sub.3 and Li.sub.3 N.
FIG. 5 is an X-ray diffraction pattern elicited from the solid products of the solid-state metathesis reaction at 45 kbar of Gal.sub.3 and Li.sub.3 N.
FIG. 6 shows the photoluminescence spectra at 298 K and 20 K of a GaN sample produced at 45 kbar.
DESCRIPTION
It has been discovered that high quality, pure, refractory crystalline materials, particularly refractory nitrides and more particularly gallium nitride, can be produced by a solid-state exchange (metathesis) reaction when conducted in a controlled environment at high pressures with initial temperatures being ambient. FIG. 1 shows an apparatus 10 used for performing this reaction. The apparatus 10 is a hydraulic press which includes an upper
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Kaner Richard B.
Wallace Charles H.
Langel Wayne
Ram Michael J.
The Regents of the University of California
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