Modeling of zinc-indiffusion-induced disordering of GaAs/AlAs superlattices
A model for the effect of Zn indiffusion on enhancing the GaAs/AlAs superlattice (SL) disordering process, which combines recently proposed models for Ga self-diffusion and Zn diffusion in GaAs, is presented. Four coupled partial differential equations describing the process were solved numerically. Satisfactory agreement between the simulated results and experimental data available in the literature is obtained. At a given temperature, the used values for the diffusion coefficient and the thermal equilibrium concentration of the responsible point defect species, the doubly positively charged Ga self-interstitials IGa2+, are a consistent splitting of the known Ga self-diffusion coefficient dominated by IGa2+. Quantitatively, the SL disordering enhancement is mainly due to the Fermi-level effect while an IGa2+ supersaturation also makes a small contribution. Because of p-doping by Zn acceptor atoms, the IGa2+ concentration is increased tremendously via the Fermi-level effect. An IGa2+ supersaturation also develops because the IGa2+ generation rate is higher than its removal rate. The enhanced SL disordering process mainly proceeds under the Ga-rich SL composition conditions. The Zn-indiffusion-enhanced Al-Ga interdiffusion coefficient shows an apparent dependence on the Zn s- concentration differing slightly from a quadratic relationship.
Zimmermann, H; Gösele, U; Tan, TY
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