Beryllium diffusion in InGaAs compounds grown by chemical beam epitaxy

Be diffusion mechanisms during post-growth annealing have been investigated in p-type InGaAs epitaxial layers. These Be-doped InGaAs layers were grown between two undoped InGaAs layers. Annealing cycles with time durations of 30 s to 3 min and temperatures in the range of 500-800 degrees C for doping concentrations of 5 x 10(18), 1 x 10(19) and 3 x 10(19) cm(-3) were performed. It was found that there is no significant Be diffusion during post-growth rapid thermal annealing (RTA) for all doping levels if annealing is performed at 500 and 600 degrees C for a time under 1 min. The same observation was made for a Be concentration of 5 x 10(18) cm(-3) with annealing at 700 degrees C for 30 s. For a doping level of 3 x 10(19) cm(-3), significant Be diffusion occurs for temperatures and durations greater than 700 degrees C and 1 min respectively. The shapes of the obtained curves represent a 'double profile' giving rise to a concave region called a 'kink'. It was deduced from the experiments that the Be effective diffusion coefficient is approximately constant for the high region of the concentration profiles and proportional to the square root of concentration for the low part of the experimental curves. Assuming the latter coefficient dependence, an effective diffusivity was substituted into Fick's second law and the resulting differential equation was solved numerically using an explicit finite-difference method. Good agreement was obtained between our depth profiles and the corresponding simulated distributions.