The Zn was introduced by using the electron beam doping method. That is, a Zn sheet was sandwiched between GaAs wafers and the surface of the GaAs was irradiated with 7MeV electrons. The use of secondary ion mass spectroscopy revealed U-shaped diffusion profiles for impurities in the substrates. The results could be explained in terms of the kick-out mechanism, and surface diffusion processes.

U-Shaped Diffusion Profiles of Zn Atoms in GaAs by Electron Beam Doping. A.Takeda, T.Wada: Materials Science Forum, 1994, 143-147, 1421-6