The diffusion of Be was considered in heavily-doped p-type structures which had been grown using molecular beam epitaxy. Secondary ion mass spectrometric measurements, performed on samples which had undergone rapid thermal processing (850C, 30s), showed that Be diffusion was faster in p/p+/p structures than in p/p+ ones and that an increase in the As4/Ga flux ratio during molecular beam epitaxial growth affected Be diffusion only in the p/p+ structures. The results were investigated by modeling Be diffusion as a substitutional–interstitial diffusion mechanism in which Be transition from substitutional to interstitial took place via a kick-out process. The modeling procedure, previously used to simulate Be and Zn diffusion in GaAs and related compounds, was modified in order to account for a lack of equilibrium in the initial concentration of Ga interstitials. It was shown that, when the lack of equilibrium was accounted for at the beginning of annealing, a satisfactory description of the secondary ion mass spectrometry results was achieved in both p/p+ and p/p+/p structures. Samples which were grown using different As4/Ga flux ratios were also considered. The model results permitted led to the conclusion that, in p/p+/p structures, the concentration of point defects (e.g., IGa) in regions cladding the base-layer affected to a major extent the Be diffusion during rapid thermal processing. Therefore, an efficient reduction in Be diffusivity was expected only when the entire structure was grown using high V/III flux ratios.

Be Diffusion in Molecular Beam Epitaxy-Grown GaAs Structures. R.Mosca, P.Bussei, S.Franchi, P.Frigeri, E.Gombia, A.Carnera, M.Peroni: Journal of Applied Physics, 2003, 93[12], 9709-16