Abstract

The relaxation of a submonolayer step concentration profile of Sb on Ge(111) has been imaged directly by using a newly developed microscopy based on surface second harmonic generation. The step is created in ultrahigh vacuum near room temperature with a beam source and retractable mask. The sample is heated to the diffusion temperature (~800 K) so that the step relaxes. After quenching back to room temperature to freeze the profile, the entire profile is illuminated with a pulsed laser and the reflected second harmonic light is imaged into a photodiode array. SH yield vs. coverage is calibrated independently with Auger spectroscopy. Boltzmann-Matano analysis of the diffusion profile yields the coverage dependence of the diffusivity D. This method avoids the surface damage problems often associated with related laser desorption/grating techniques. We find that D decreases by an order of magnitude as the coverage increases, with a diffusional activation energy near 2 eV. The significance of these results for dopant incorporation chemistry in Ge molecular beam epitaxy is discussed.

© 1992 Optical Society of America