MEL LOCH ET AL quality single crystals. These materials are arsenides such as GaAs, AIGaAs, and InGaAs containing arsenic clusters. The composites are formed by incorporating excess arsenic in the semiconductor, which per cipitates in the anneal. The incorporation of the excess arsenic is accomplished by molecular beam epitaxy at low substrate temperatures. The cluster density can be controlled with the coarsening annealing. The positioning of the clusters can be controlled with heterojunctions and doping. These composites exhibit several interesting properties, including high-resistivity, appreciable optical absorption below the band gap of the semiconductor matrix material, a large electro-optic effect, and very short carrier lifetimes.

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Room-temperature deep-ultraviolet emission has been observed from Al 0.13 Ga 0.87 N/Al 0.10 Ga 0.90 N double heterostructure light-emitting diodes (LEDs) on (0001)-oriented sapphire substrate. By introducing undoped barrier layers, which sandwich the active layer, the LED was operated at a peak emission wavelength of 339 nm with a narrow linewidth of 5.6 nm. The dependence of emission intensity on injection current suggests that the nonradiative recombination was suppressed and the diffusion current for the recombination process was dominant at the injection current of over 20 mA.

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