OPTICAL-PROPERTIES OF BISMUTH-TERMINATED GAAS(110) SURFACES

We have investigated the room temperature deposition of ultrathin bism uth layers on GaAs(110) surfaces by using Surface Differential Reflect ance (SDR) spectroscopy. In SDR spectra measured at the ''as grown'' s urfaces, optical transitions related to the new electronic structure o f the overlayer appear at 0.8 eV and 1.35 eV, below the gap of bulk ga llium arsenide. Because of their energy position and dependence upon d eposited Bi thickness, we interpret them as related to Bi-overlayer an d Bi-substrate bonds, respectively. Subsequent annealings of the overl ayer at temperatures in the range 200-350 degrees C have not produced any improvement in the quality of the interface, but a new tweak) tran sition at about 1.1 eV possibly related to Bi crystallites present at the surface. Annealing at T > 350 degrees C produces desorption of the adsorbed bismuth.