THE EFFECT OF THE GROWTH-RATE ON THE LOW-PRESSURE METALORGANIC VAPOR-PHASE EPITAXY OF GAAS GE HETEROSTRUCTURES

GaAs/Ge heterostructures for solar cell applications were grown by low-pressure metalorganic vapour phase epitaxy and their morphological and structural properties were studied by different characterization techniques including X-ray diffraction and topography, scanning electron microscopy, transmission electron microscopy and photoluminescence. A study of the initial growth stages evidenced that a high growth rate (10 mum/h) gives a better surface morphology than a lower one (2 mum/h), owing to the fact that the growth islands characteristic of the initial deposition stages are smaller with homogeneous size and spread at high density. Below the critical thickness threshold for the generation of misfit dislocations, the epilayers grown under low-rate conditions are affected by the presence of twins propagating from the interface into the layer; on the contrary, twins were never observed in the case of the high growth rate. Moreover, indirect information about the interdiffusion processes trough the layer-substrate interface were obtained; it was found that the interdiffusion is probably much more effective in the case of the low growth rate.