Optical anisotropy of the (100) surfaces in AlxGa1-xAs ternary compounds

The reflectance anisotropy spectra of the clean (100) surfaces of the AlxGa 1- xAs ternary compounds at aluminum concentrations 0 less than or equal to x less than or equal to 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 tra nsitions in the arsenic dimers dominates in the spectra of the clean arseni c-terminated GaAs surfaces. For the ternary compounds, an increase in the a luminum concentration brings about the broadening of this signal and its sh ift toward the low-energy range. This is explained by the appearance of add itional signals associated with the optical transitions in the nonequivalen t 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 gall ium atoms leads to a decrease in the energy of optical transition in the di mer. The fundamental optical transition energies are determined for the non equivalent dimers. (C) 2000 MAIK "Nauka/ Interperiodica".