Effect of encapsulant material on the diffusion of beryllium in molecular beam epitaxy gallium arsenide

Experiments were done that illustrate the role of the wafer surface in the transient diffusion of Be in GaAs. Samples were doped during molecular beam epitaxial growth and annealed at 900 °C for 15 min and 2 h under two different caps. In some of the annealed samples, the dopant was initially located near the surface. Other samples had the dopant initially located in a buried layer. Both types of samples were analyzed by secondary ion mass spectrometry measurement. The variations in the diffusion behavior for these different experimental conditions can all be qualitatively explained by a model which accounts for three important effects: the transient evolution of point defect populations; the injection of Ga vacancies by an oxide cap; and the efficiency of the surface in restoring point defect equilibria.