Orientation and preparation dependence of steps and defects on GaAs

Abstract

The distribution of steps and defects has been studied on a cylinder-sector shaped GaAs crystal exposing continuously all orientations between (110) and (111) Ga. We used a spot profile analysis LEED system with high transfer width. The sample was prepared either by ion bombardment and annealing (IBA) or by molecular beam epitaxy (MBE). After MBE preparation, the concentration of point defects is considerably reduced on all orientations. At (111), we find steps one GaAs double layer high. The average distance between the steps increases after MBE thus indicating a smoothening of the surface. On vicinal orientations near (111) towards (110), steps two Ga-As double layers high form in addition. In the vicinity of (110) towards (111), both single and double layer steps appear. The relative amount of double layer steps increases upon MBE preparation and with increasing deviation from the (110) orientation. This is in agreement with former oxygen adsorption results. It is confirmed that double layer steps represent the more stable configuration. Intermediate orientations (e.g. (331) or (221)) do not form specific structures but consist of mixtures of, most likely stepped, (111) and (110) facets.