Optical anisotropy of the (100) surfaces in AlxGa1−x As ternary compounds

Abstract

The reflectance anisotropy spectra of the clean (100) surfaces of the AlxGa1−xAs ternary compounds at aluminum concentrations 0≤x≤0.5 have been measured and thoroughly studied. In the spectral range from 1.6 to 3.5 eV, the signal caused by the optical transitions in the arsenic dimers dominates in the spectra of the clean arsenic-terminated GaAs surfaces. For the ternary compounds, an increase in the aluminum concentration brings about the broadening of this signal and its shift toward the low-energy range. This is explained by the appearance of additional signals associated with the optical transitions in the nonequivalent arsenic dimers, in which a part of the Ga atoms in the bulklike bonds is replaced by the Al atoms. An increase in the number of the substituted gallium atoms leads to a decrease in the energy of optical transition in the dimer. The fundamental optical transition energies are determined for the nonequivalent dimers.