STUDY OF DEPOSITION DEPENDENT CHARACTERISTICS OF GOLD ON N-GAAS BY PHOTOREFLECTANCE SPECTROSCOPY

We used the noncontact electric field modulation technique of photoref lectance to study the effect of gold on GaAs grown by two different me talization methods. A semitransparent 7 nm gold overlayer was grown on low doped n-GaAs (2 x 10(16) cm(-3)) using metalization by evaporatio n and by sputtering. Our experimental results indicate that the photor eflectance lineshape depends on the metalization method in a character istic way. We present evidence of a previously unreported modulation m echanism in photoreflectance. We employed simulation of photoreflectan ce lineshape based on a multilayer model to reproduce characteristic f eatures of experimental lineshapes. For sputtered Au/GaAs samples the best simulated lineshape was obtained through an unusual modulation, w hich is based on a strongly pined surface electric field. This produce d a lineshape somewhat similar to a third derivative functional form w ith severely suppressed Franz-Keldysh oscillations (FKO). Simulation w ith the same set of parameters and a parallel field modulation restore d FKO and reproduced the experimental lineshape of the evaporated Au/G aAs. The parallel field modulation spontaneously reproduced the below- band-gap feature, which is often observed in electromodulation spectro scopy. We believe the change in FKO is correlated with the density of interface states as they influence the extent of Fermi-level pinning. (C) 1997 American Institute of Physics.