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 400 degr ees C on GaAs(001)c(4 x 4) surfaces under an excess As or Al flux. Similar growth conditions are used by some workers to fabricate Si interlayers in m etal/GaAs diodes and to modify the Schottky barrier. We investigated the mi crostructural changes caused by the expected large As or Al incorporation i n the Si layers. We found that Si epitaxial layers grown under an As flux h ave a structure similar to that of control samples in which the Si layer wa s grown in the absence of any excess anion or cation flux. Surprisingly, th e only microstructural modification induced by the excess As is a somewhat higher density of extended defects at the interface. Conversely, the use of an excess Al flux during growth yields large microstructural modifications relative to the control samples. A relatively thick, highly disordered qua ternary layer appears to form on most of the surface, while Ga islands are also observed, sometimes with the inclusion of Al clusters.