Abstract
Migration of surface adatoms is effectively enhanced by evaporation Ga or Al atoms onto a clean GaAs surface under an As-free atomosphere. This characteristic is used to develop “migration-enhanced epitaxy” by alternately depositing Ga and/or Al atoms and As 4 molecules to the substrate surface. It has been found that migration-enhanced epitaxy is useful for growing high-quality GaAs and AlGaAs layers at very low substrate temperatures. The investigationof the growth mechanism by reflection high-energy electron diffraction revealed that a flag growing surface is maintained during migration-enhanced epitaxy, even when the number of Ga or Al atoms deposited per cycle is not exactly adjusted to the number of surface sites. It was also found that the composition at the growing surface can deviate considerably from stoichiometry at low growth temperatures because of an excess As adsorption. The deviation from stoichiometry on the growing surface deteriorates the photoluminescence efficiency of the grown layer, and makes the layer structure unstable in thermal annealing. This problem was shown to be avoidable by optimizing the number of As 4 molecules deposited per cycle.
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