Optical characterization of indium-terminated GaAs(001) surfaces

We have investigated the growth of thin indium layers on As- and Ga-terminated GaAs(001) surfaces by reflectance anisotropy spectroscopy (RAS), low energy electron diffraction (LEED), and auger electron spectroscopy. Room temperature deposition of indium on the $(2\mathrm{}\times 4)/c(2\times 8)$ surface and subsequent annealing at 450 °C leads to the formation of an In-terminated surface showing a $(4\mathrm{}\times 2)$ LEED pattern, accompanied with strong changes in the measured surface optical anisotropy. When indium is deposited onto the $(4\mathrm{}\times 2)/c(8\times 2)$ surface, on the contrary, the $(4\mathrm{}\times 2)$ In-terminated surface is already formed at room temperature deposition without needing annealing, as demonstrated by the RAS spectra. The finding that almost identical RAS spectra and $(4\mathrm{}\times 2)$ LEED patterns are obtained in both cases shows that the same final atomic structure is achieved. Finally, we conclude that the structure of the In-terminated surface is similar to that of the clean Ga-rich surface, although a more detailed model would need accurate calculations of the microscopic origin of the measured anisotropy.