Abnormal out-diffusion from heavily Be-doped material, prepared by molecular beam epitaxy, was found to be initiated by a decrease in the lattice constant of the p+ epilayer. From double-crystal X-ray spectra, Van der Pauw measurements, photoluminescence data, and infra-red absorption spectra for Be-doped material with various dopant concentrations, it was deduced that there existed a critical doping concentration (2.6 x 1019/cm3) beyond which the lattice constant of the epilayer began to decrease, and Be out-diffusion into the substrate was significantly enhanced. It was suggested that the tensile stress on the epilayer resulted in abnormal Be out-diffusion. The absorption coefficient, in the 8 to 10 region, of Be-doped material with a carrier concentration of 8.3 x 1019/cm3 was found to be about 104/cm.

B.D.Liu, T.H.Shieh, M.Y.Wu, T.C.Chang, S.C.Lee, H.H.Lin: Journal of Applied Physics, 1992, 72[7], 2767-72