Interface shape and crystallinity in LEC GaAs

Abstract

Growth striation mapping was used to relate the growth interface shape to crystallinity failure modes in LEC growth of undoped <100> GaAs. The onset of twinning and polycrystallinity were both found to depend on the interface shape near the crystal periphery. The origins of polycrystalline growth were investigated in 8 kg, 3-inch and 4-inch diameter crystals. Interface maps of these crystals show that polycrystalline growth begins when the growth interface periphery turns down, independent of the shape of the central portions. The cause of initial grain boundary formation was found to be included gallium droplets which originate on the surface and migrate through the crystal toward the growth interface. Twinning occurs on {111} facets, usually during shoulder growth. Growth striations show that the sequence of events leading to twin formation consists of deep facet growth, followed by meltback and rapid regrowth. We found it possible to avoid twinning by reducing melt instabilities or by reducing the extent of facet growth. © 1991.