Coherent light generators – Particular active media – Semiconductor
Patent
1992-06-29
1994-06-14
Davie, James W.
Coherent light generators
Particular active media
Semiconductor
H01S 319
Patent
active
053217136
DESCRIPTION:
BRIEF SUMMARY
axy of Gallium Nitride on Sapphire Substrate" by Amano, et al, THIN SOLID FILMS, Vol. 163, pages 415-420, 1988. Whereas the former reference utilized molecular beam epitaxy, the latter reference utilized metalorganic vapor phase epitaxy to achieve a gallium nitride film with a smooth surface, free from cracks, on a sapphire substrate.
Another apparatus and method for growing a single crystalline GaN film was reported in "P-Type Conduction in Mg-Doped GaN treated with Low Energy Electron Beam Irradiation (LEEBI)", by Amano, et al., in the Japanese Journal of Applied Physics, Vol. 28, No. 12 (December, 1989), pp. L2112-L2114. Amano, et al, utilized a horizontal type metalorganic vapor phase epitaxy reactor at atmospheric pressure with a trimethylgallium source. The particular residence times of each step in the growth process were not disclosed, however.
The use of Gallium Nitride materials in a light emitting application within the ultraviolet region is reported by Amano, et al, "Stimulated Emissions Near Ultraviolet at Room Temperature from a Gallium Nitride Film Grown on Sapphire by Metalorganic Vapor Phase Epitaxy using an Aluminum Nitride Buffer Layer", Japanese Journal of Applied Physics, Vol. 29, No. 2, pages L205-L206, February 1990. In this Amano, et al reference, the metalorganic vapor phase epitaxy system operated at atmospheric pressure and resulted in a gallium nitride film that is approximately 31/2 micrometers thick residing on an aluminum nitride interface with a depth of approximately 50 nanometers, the latter residing on a sapphire substrate of approximately 250 micrometers in thickness. This resulted in a gallium nitride film having a carrier concentration of about 2.times.10.sup..intg. per cubic centimeter at room temperature and an electron mobility of approximately 350 square centimeters per volt second at room temperature.
In the Amano paper emissions from CaN were reported. However, no information was given regarding the use of GaN/mirrors, etc., to create an actual laser, rather than a mere light emitter.
Finally, Kahn et al. reported on the photoluminescent characteristics of quantum wells composed of an AlGaN-GaN-AlGaN structure, in Applied Physics Letters, Vol. 56, pp. 1257-1259, Mar. 26, 1990. These quantum wells were grown on basal plane sapphire by low pressure metalorganic vapor deposition. The photoluminescence spectrum showed a peak emitted light intensity near the region having a wavelength of approximately 3400 angstroms.
Ideally, the ability to deposit gallium nitride materials in a controllable and precise manner would permit the development of a family of solid state optical devices, such as filters and ultraviolet lasers. Despite the efforts of previous researchers, ultraviolet lasers continue to be physically large and difficult to operate, requiring the use of high purity gasses which must be vented from the laser apparatus and the building housing the laser apparatus.
3. SUMMARY OF THE INVENTION
The present invention resides in an apparatus and method for creating high quality single crystal gallium nitride layers over basal plane sapphire substrates and a family of optical devices fabricated therefrom. A low pressure metalorganic chemical vapor deposition technique is used which results in materials having carrier densities as low as 10.sup.17 per cubic centimeter at room temperature with corresponding electron mobilities of approximately 300 square centimeters per volt second. The photoluminescence line widths are as narrow as three nanometers. Narrow bandwidth filters are created by depositing quarter wavelength laminates, or stacks, of Al.sub.y Ga.sub.l-y N/Al.sub.x Ga.sub.l-x N, where x and y have values between zero and one. The improved gallium nitride material permits the construction of improved optical devices, including mirrors, quantum wells, and lasers. In particular, the present invention includes a solid state ultraviolet laser, thereby providing an efficient, compact, rugged and lightweight alternative to prior art ultraviolet laser devices.
4.
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Khan Muhammad A.
Olson Donald T.
VanHove James M.
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