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We prepared ultrafine germanium particles by gas-evaporation techniques. The particle composition was studied by Raman and x-ray scattering. We take an analytical model to explain the Raman profile: the particle is composed of a single-crystalline core and a coating amorphous shell. In this single-crystalline part, the phonon mode is completely localized, and as a result the red shift and the broadening of the Raman signal are induced. We introduce a localization factor to describe the size effect. According to this model we determined the mean diameter of a crystalline particle. The result is compared with that from x-ray diffraction. Our results indicate that the coating amorphous shell thickness is nearly constant, although the crystalline particle size varies by the evaporation-gas pressure. Furthermore, we found that the Raman profile changes by the wavelength of the exciting laser.

Photoreflectance (PR) spectroscopy has been used to study the surface Fermi level in GaAs by taking account of photovoltaic properties at the semiconductor surface. The PR signal amplitude ‖ΔR/R‖ is proportional to a modulating photovoltage Vm generated by a modulation light irradiation. To modify the surface potential, the sample was irradiated by a third perturbing light, i.e., a continuous bias light Pb, together with the modulation light. The modulation light power dependence of ‖ΔR/R‖ is extremely sensitive to bias light intensity, surface Fermi level, and temperature. From the analysis of the temperature dependence of ‖ΔR/R‖ on modulation-light power, the surface Fermi level of 0.47±0.09 eV below the conduction band was determined for a molecular beam epitaxially-grown GaAs(100).

Anisotropic optical transitions in an ordered Ga0.5In0.5P alloy semiconductor have been studied by electroreflectance (ER) polarization spectroscopy. The atomic ordering of column-III sublattices causes a splitting of the valence-band maximum into two doubly degenerated levels at k=0. The ER spectra reveal signals originated from the Γ6c-Γ4v, Γ5v and Γ6c-Γ6v transitions caused by the ordering. The [110] and [11̄0] ER signals due to the Γ6c-Γ6v transition show strong anisotropic characters of their intensity and line shape. On the other hand, the signal due to the Γ6c-Γ4v, Γ5v transition changes only in the intensity by the polarization direction. The ER intensities measured at various polarization angles follow the theoretically derived trends based on the selection rule for electronic-dipole transitions in the ordered crystal.