Rapid thermal annealing was used to diffuse Zn into GaAs from a thin-film zinc silicate source that was prepared by chemical vapour deposition at atmospheric pressure. Comparisons were made with conventional open-tube furnace annealing, for a diffusion temperature of 650C. The diffusivities were found to be similar; in contrast to previous results. At temperatures ranging from 650 to 750C, sharp Zn diffusion profiles were observed. At temperatures above 750C, kinks in the diffusion profiles were found. Such kinks were also observed when semi-insulating substrates were used instead of Si-doped n+-type substrates. A model for Zn diffusion had already been developed, and this was based upon the pairing of interstitial Zn with all of the acceptor species which were present during diffusion. The predominant species were found to be substitutional Zn, and Ga vacancies. The concentration of the latter was a function of the background dopant concentration. The results of the model were shown to agree with all of the present experimental evidence, and were also consistent with the experimental observation of 2 distinct activation energies for Zn diffusion into n+-doped substrates. These energies were equal to 1.1 and 2.6eV for temperatures which were above or below about 790C, respectively.

G.Rajeswaran, K.B.Kahen, D.J.Lawrence: Journal of Applied Physics, 1991, 69[3], 1359-65