The concentration-dependent diffusion of Zn during metalorganic vapor-phase epitaxy from a Zn-doped InP layer, and into the adjacent undoped InP buffer layer, was studied by means of secondary ion mass spectroscopy and carrier concentration profiling. If the growth rate of the Zn-doped film was faster than the interdiffusion of Zn into the underlying undoped buffer layer, the diffusion problem could be treated as a 1-dimensional couple between 2 semi-infinite media. Also, Zn diffusion under optimum growth conditions completely eliminated the thermal decomposition problem which was encountered when using sealed-ampoule or open-tube methods, and also retained all of the intrinsic point defects in their thermodynamic equilibrium concentrations. When using an optimum growth temperature of 625C, and a maximum Zn flow that was below the incorporation limit for substitutional Zn (in order to ensure that the Zn was incorporated substitutionally), the diffusion profiles of Zn across the interface could be simulated by assuming a concentration-dependent diffusivity. A third-power concentration dependence of the effective diffusion coefficient was found. This applied to both Frank-Turnbull and kick-out equilibrium mechanisms for an interstitial-substitutional diffusion model. This indicated a 2+ charge state for the fast-diffusing Zn interstitials. Extrapolations into the high-concentration regime of sealed-ampoule experiments generally agreed with published data, although the predominant Zn atoms which were found in the high-concentration regime formed complexes with P vacancies in a neutral state.

Concentration Dependent Zn Diffusion in InP during Metalorganic Vapor Phase Epitaxy. S.N.G.Chu, R.A.Logan, M.Geva, N.T.Ha: Journal of Applied Physics, 1995, 78[5], 3001-7