ON THE SUBLATTICE LOCATION OF GAAS GROWN ON GE

Single domain GaAs layers have been grown by atmosphere pressure metal-organic vapor phase epitaxy on Ge(100) substrates misoriented to (111) with different angles of 0° -4°, under various growth conditions. Epilayers have been studied by transmission electron microscopy, molten KOH etch and optical interference contrast microscopy. It is found that at an initial growth temperature of 550°C the sublattice location of the GaAs layers grown on substrates with small misorientation angles (less than 3°) is reversed as compared to that of the layers grown on substrates with larger misorientation angles, independent of the initial growth rates and V/III ratios. When the initial growth temperature is increased the transition from one type of sublattice location to the other occurs at a lower misorientation angle, while at an initial growth temperature of 700°C the sublattice location of the layers grown on the different substrates becomes the same. These results can hardly be explained by the existing theories and a new model is proposed based on a concept that the sublattice location of GaAs on Ge is defined by the relative intensity of nucleation at steps and on terraces between steps, taking into account the effects of the growth temperature and the step density of the substrate surface on the nucleation mode, and the fact that single domain GaAs can be obtained by the self-annihilation of antiphase boundaries.