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Growth of Aluminum Gallium Nitride Thin Films for Electro-Optic Device Applications.

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Final rept. 6 Sep 77-15 Feb 81,

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Highly p-doped AlGaN offers the prospect of very efficient and sharp-cutoff solar-blind photocathodes, as well as near-UV solid-state lasers. However, AlN reported to date has been semi-insulating, and GaN has been semi-insulating or n-type. Spontaneous generation of compensating N-vacancy donors is believed responsible for the inability to p-dope GaN. In this work, GaN was deposited on sapphire by reaction of Ga with a high-pressure 100 Pa N2 plasma over the substrate. High plasma pressure and low substrate temperature were used in order to inhibit N-vacancy formation. Be, a likely and low-volatility p-dopant, was co-deposited. After it proved impractical to introduce Ga into the N2 plasma by evaporation, it was sputtered in a 100 Pa DC N2 plasma with much better success. Epitaxy of updoped films was obtained at 700 C, although films doped to 4 - 6 x 10 to the 20th power Becc were polycrystalline. All films turned out n-type by thermoelectric probing and exhibited a large activation energy for conduction, indicating the dominance of unintentional deep impurities. Undoped films had resistivities of 400,000 ohm-cm at 300 C and 20,000 ohm-cm at 600 C. Be doping increased conductivity by X100 and appeared to be acting as a deep donor. A cleaner sputtering environment and closer Be control are recommended in the further pursuit of p-type GaN. Author

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  • Solid State Physics

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