Complementary DSL, EBIC and PL study of grown-in defects in Si-doped GaAs crystals grown under Ga- and As-rich conditions by LEC method

Local environments (Cottrell atmospheres) of grown-in dislocations in Si-doped LEC GaAs crystals were examined by three independent high spatial resolution techniques: DSL (diluted Sirtl-like etchant with light) photoetching combined with surface step profiling, photoluminescence (PL) and energy-dependent electron beam induced current (EBIC) mode of the scanning electron microscope (SEM). The GaAs samples were taken from two ingots grown under Ga- and As-rich conditions both with comparable Si doping level (4x1017 cm-3). The chemical composition and consequently the point defect equilibrium within the Cottrell atmospheres was found to be essentially different in the two crystals. It has been clearly recognized by step profiling after DSL photoetching that in As-rich crystals elevated plateaus are formed whereas in Ga-rich GaAs complex depressions appear in the vicinity of dislocations. This corresponds to a decrease and increase of the etching rate, respectively, i.e., indicates essential difference in the number of holes available for surface reaction during DSL photoetching. On the basis of data obtained from EBIC measurements, PL mappings and spectral analyses, models are proposed which explain the observed morphological differences after photoetching.