Temperature dependence and origin of InP(100) reflectance anisotropy down to 20 K

InP(100) surfaces were investigated by reflectance anisotropy spectroscopy (RAS) in the temperature range between 20 and 840 K. Surfaces were prepared via metal-organic chemical vapor deposition (MOCVD) resulting in P-terminated (2x1)-like and In-terminated (2x4) reconstructions. Additionally, intermediate states of different phosphorus coverage were prepared. RA spectra were recorded bath inside the MOCVD reactor and in an ultrahigh vacuum chamber. At low temperatures, features in the RA spectra sharpened significantly due to the reduced lattice vibrations and electron-phonon interactions. The temperature-dependent energy shift of specific RAS features was determined between 20 and 840 K, and fitted with a model containing the Bose-Einstein occupation factor for phonons. The respective fitting parameters were compared to those of the InP bulk critical-point transitions nearby. Careful data analysis provided evidence for surface transitions and surface modified bulk transitions in the RA spectra.