Growth of ZnSe/GaAs Superlattices by Migration-Enhanced Epitaxy

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Abstract
ZnSe/GaAs superlattices are grown on (001)-oriented GaAs substrates by migration-enhanced epitaxy. By this method, high-quality GaAs layers can be grown on GaAs substrates at temperatures as low as 250°C, which corresponds to the optimum growth temperature of ZnSe. However, the extremely low sticking coefficient of As4 onto a ZnSe surface deteriorates the crystal quality of GaAs on ZnSe. To solve this problem, GaAs growth on ZnSe is initiated by As4 deposition at room temperature. A few atomic layers of Ga are then deposited. After annealing at 250°C, GaAs growth is continued by migration-enhanced epitaxy. This method produces superlattices with a low density of dislocations and defects. Transmission electron microscope observation of the superlattice shows the GaAs growth rate per one cycle of alternately supplied Ga and As4 to be almost constant throughout a superlattice growth of 12 periods. However, the ZnSe growth rate per one cycle of alternate Zn and Se deposition increases from about 0.35 monolayer in the first period and tends to saturate at about 0.5 monolayer at the particular growth temperature of 250°C. To explain this, a missing Zn array structure of the c(2×2) reconstructed structure is proposed along the [100] and [1̄00] directions.