Transmission electron microscopy studies of the microstructure of Si layers grown on GaAs(001) under an excess As or Al flux

Si layers with nominal thickness of 30± 40 monolayers were grown at 4008C on GaAs(001)c(4 £ 4+ surfaces under an excess As or Al ? ux. Similar growth conditions are used by some workers to fabricate Si interlayers in metal/GaAs diodes and to modify the Schottky barrier. We investigated the microstructural changes caused by the expected large As or Al incorporation in the Si layers. We found that Si epitaxial layers grown under an As ? ux have a structure similar to that of control samples in which the Si layer was grown in the absence of any excess anion or cation ? ux. Surprisingly, the only microstructural modi® cation induced by the excess As is a somewhat higher density of extended defects at the interface. Conversely, the use of an excess Al ? ux during growth yields large microstructural modi® cations relative to the control samples. A relatively thick, highly disordered quaternary layer appears to form on most of the surface, while Ga islands are also observed, sometimes with the inclusion of Al clusters.