Crystallographic Defects in (001) GaAs Epitaxial Layers Grown by MOCVD

Abstract

The influence of various MOCVD growth parameters, substrate preparation, and substrate misorientation on the formation of crystallographic defects during epitaxial growth of has been studied. Low arsine/TMG ratios during growth lead to the formation of so‐called oval defects, which generally are growth hillocks with a polycrystalline inclusion. Local arsenic deficient/gallium rich surface areas are concluded to be responsible for the formation of these defects. Low growth temperatures (<660°C) were found to lead to so‐called boat defects, which generally contain a deformed region with dislocations, stacking faults, and, sometimes, polycrystalline material, and a defect free part. Their formation is related to impurity adsorption at the growing surface. On exactly oriented crystals, growth plateaus with a flat top have been observed occasionally. These hillocks are shown to contain numerous dislocations. High velocities of growth steps in combination with impurities at the substrate surface are concluded to be the most probable cause for their formation. Surface work damages are shown to lead to formation of dislocations in the epitaxial layers. It is shown that annealing before growth strongly reduces the number of these work damage related surface defects. The structure of the above groups of defects has been studied in detail by defect selective etching and optical‐ and electron microscopy. Their origin has been studied by a systematic variation of growth conditions. The original substrate surface appears to play an important role in the formation of most defects. Some conclusions are drawn about the morphology of the defects from a consideration of the (001) surface structure.