Initial growth layers and critical thickness of InAs heteroepitaxy on GaAs substrates

The initial growth layers and the critical thickness of InAs on GaAs are investigated in order to establish which growth modes and heteroepitaxial processes can be revealed. The InAs layers are grown on (001)-oriented GaAs substrates at 480 degrees C by molecular beam epitaxy, They grow two-dimensionally at first and then begin to develop three-dimensional growth at a 1.8 mono-molecular layer (ML). The experiments suggest that the first flat layer remains at and just after three-dimensional formation and thus the growth mode is of Stranski-Krastanov. The experimental results show that the critical thickness is 3 ML beyond which misfit dislocations are generated in the layers and/or at the heterointerface. They are observed and measured by reflection high energy electron diffraction, atomic force microscopy, electroluminescence, photocurrent spectroscopy, transmission electron microscopy, and photoluminescence. The critical thickness is theoretically obtained by taking account of the strain energy calculated by the valence-force field method. The experimental thickness agrees well with the theoretical value.