High-resolution diffraction utilizing an analytical electron microscope has been employed to identify small (∼500 Å-diam) precipitates attached to line dislocations in gallium arsenide. The results show that the precipitates consist of crystallites of elemental hexagonal arsenic embedded within the gallium arsenide matrix. Precipitates were observed in a range of semi-insulating, p-type, and n-type material and were not dependent on the presence of specific additional dopants for their occurrence. The way in which the particles may originate is discussed.

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Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2 X 102' cm -3, to elucidate profile control and electrical activation over the growth temperature range 450-900 "C. Precipitation and surface segregation effects were observed at doping levels of 2 X 102' cm -3 for growth temperatures above 600 "C. At growth temperatures below 600 "C, excellent profile control was achieved with complete electrical activation at concentrations of 2 x 102' cm -3, corresponding to the optimal MBE growth conditions for a range of Si/Si,Gel --x heterostructures.