It was noted that substitutional Zn was linearly incorporated into device-quality material under low Zn-source flow-rates during atmospheric-pressure metalorganic vapor-phase epitaxy at 625C. It saturated at about 4 x 1018/cm3 under high Zn-source flow-rates. An increase, in the Zn-source flow-rate, to beyond saturation significantly increased the amount of interstitial incorporation. The excess interstitials diffused into the undoped region via an interstitial-substitutional diffusion mechanism, and revealed themselves via an enhanced diffusivity. It was recalled that a model had previously been proposed, for surface adsorption-desorption trapping during substitutional Zn incorporation, in which the saturation level was assumed to be governed by surface incorporation sites for substitutional Zn. This model was applied here, to interstitial Zn incorporation at Zn source flow rates which were above the saturation level for substitutional Zn, in order to explain the enhanced Zn diffusion. The analysis was extended so as to include the incorporation of neutral Zn in the presence of excess P vacancies. It was concluded that this model could be used for the simultaneous incorporation of Zn of all 3 types during epitaxy; provided that the incorporation processes were independent.

S.N.G.Chu, R.A.Logan, M.Geva, N.T.Ha, R.F.Karlicek: Journal of Applied Physics, 1996, 80[6], 3221-7