PHOTOREFLECTANCE STUDY OF THE LONG-TERM STABILITY OF VARIOUS SURFACE CHEMICAL TREATMENTS ON (001)N-GAAS

A study of the long-term stability of etching, photowashing, and sulfi de passivation [using (NH4)(2)S] treatments performed on GaAs surfaces using photoreflectance spectroscopy is reported in this paper. Dramat ic changes in the intensity of excitonic features of bulk n-GaAs quali tatively show much greater stability of sulfide-passivated than either etched or photowashed surfaces. We have also quantified the electric field in structures containing a thin, undoped GaAs layer over a highl y doped n-GaAs buffer layer using strong Franz-Keldysh oscillations pr esent in photoreflectance measurements. The results show a gradual deg radation of the effects of etching and photowashing GaAs surfaces over a period of several months, while sulfide-passivated samples remain s table and, in some sense, ''unpinned'' over this same time period.