Direct optical measurement of surface dielectric responses: Interrupted growth on (001) GaAs

Anisotropies of the visible-near-ultraviolet dielectric responses of various (001) GaAs molecular-beam-epitaxy growth surfaces are measured at temperature using a new optical double-modulation technique and a low-strain fused-quartz window. Tight-binding calculations identify structure at 1.8 eV with Ga dimers and at 2.6 and 4.1 eV with As dimers. Transient behavior on interruption of As flux is substantially altered by misorientation, suggesting substantially different terrace properties for vicinally cut surfaces.