QUANTITATIVE STUDY OF THERMAL DIFFUSION OF ELEMENTS ACROSS A ZnSe/GaAs INTERFACE USING SIMS

Abstract

ZnSe epilayers were grown on GaAs substrates, which had been treated with Se and Zn prior to the growth process. Thermal diffusion of elements across the interface was investigated, using secondary ion mass spectroscopy (SIMS). Ion-implanted standards have been used to calculate the "useful ion yield" for Zn and Se in the GaAs matrix and for Ga and As in the ZnSe matrix. Consequently, SIMS raw data were converted to quantified data. Diffusion of Ga atoms across the interface was observed for Zn-pretreated substrates. A comparison study showed that Se pretreatment of the GaAs substrate prevents thermal diffusion of Ga across the interface. This effect is believed to be due to the formation of GaAs x Se y layers at the interface, which acts as a barrier to diffusion. The Ga diffusion coefficients at annealing temperatures of 400°C, 500°C and 600°C were found to be 2.1×10-16 cm 2/s, 1.9×10-15 cm 2/s and 2.2×10-14 cm -2/s, respectively. The thermal diffusion of other elements across the interface was not observed within the resolution limit of SIMS analysis.