Elimination of gallium-source related oval defects in molecular-beam epitaxy of GaAs

Abstract

By evaporating gallium from a pBN crucible which was previously used for evaporation of Al, ‘‘Ga-spitting’’ and formation of Ga-cell related oval defects have been eliminated in molecular-beam epitaxy (MBE) of GaAs. MGE-GaAs layers as thick as 20 μm were totally free from the Ga-cell related oval defects. Remaining oval defects were those related to particulates and substrate contamination and their densities were 100 and 500 cm−2 on 5 and 20-μm thick layers of GaAs on GaAs substrates. However, these particulates related oval defects were hardly seen on up to 4-μm thick GaAs layers grown on Si substrates. Aluminum wets and reacts with the pBN crucible when heated up to 1300 °C during evaporation of Al. Condensed gallium near the orifice wets the such aluminum treated pBN surface and is not expected to spontaneously flow to the Ga charge in the form of droplets. As a result, Ga spitting does not occur and related oval defects do not form.