Quantum oscillations in the magnetoresistance of Si-doped material were analyzed in order to obtain the electron densities of the electrical sub-bands. These densities were compared with the results for self-consistently calculated sub-band structures of δ-doped material in which the spread of Si dopant atoms in the growth direction was a fitting parameter. The results indicated that there was a negligible spread in structures which were grown at substrate temperatures of up to 530C. In structures which were grown at higher substrate temperatures, there was a measurable spread. This increased with increasing substrate temperature. At a substrate temperature of 640C, the Si spread was about 22nm. An examination of the three-dimensional Si densities in these layers indicated that the predominant mechanism of Si spreading at substrate temperatures greater than 600C was the Si migration which was necessary in order to satisfy the solid solubility limit.

M.Santos, T.Sajoto, A.Zrenner, M.Shayegan: Applied Physics Letters, 1988, 53[25], 2504-6