DIRECT OBSERVATION OF PRECIPITATES AND SELF-ORGANIZED NANOSTRUCTURES IN MOLECULAR-BEAM EPITAXY-GROWN HEAVILY-DOPED GAAS-SI

We report a cross-sectional scanning tunneling microscopy investigatio n of heavily Si doped [001]-oriented GaAs grown by molecular-beam epit axy. At a very high doping level (6 x 10(19) cm(-3)), Si-doping induce d precipitates are directly observed in XSTM images of the as-grown ep itaxial layers. Most of the precipitates are found to have a character istic oval shape with the long axis (similar to 80 Angstrom) along the growth direction. In contrast to the low diffusivity of randomly dist ributed Si dopants in the moderate doping regime, these precipitates a re found to be highly mobile and spontaneously form ''nanowires'' duri ng crystal growth. (C) 1995 American Institute of Physics.