PHOTOREFLECTANCE CHARACTERIZATION OF GAAS AS A FUNCTION OF TEMPERATURE, CARRIER CONCENTRATION, AND NEAR-SURFACE ELECTRIC-FIELD

Previous measurements of the photoreflectance line shape of GaAs at the E1 transition (2-9 eV) were extended. This study covers the combined effect of temperature and carrier concentration along with a discussion of the effect of the electric field intensity and the field inhomogeneity within a depth of 20 nm from the surface. A systematic study of changes in the line shape of the above band gap transition, E1 as a function of temperature (80-400 K) and carrier concentration (CC) (2-200 X 10(16) cm-3) is presented and a model of the effect is discussed. It was found that as the carrier concentration increases beyond 1 X 10(17) cm-3, the line shape changes in phase and in broadening in a characteristic way which depends on CC and temperature. A simple correlation is established between both the broadening and the line shape rotation as a function of temperature and CC. Using the Schottky relation and Fermi-level pinning, the observed effect qualitatively was explained. Also the effect of near-surface electric field on the line shape is discussed. The observed effect may be applied as an optical measurement of the carrier concentration or possibly the electric field within a depth of congruent-to 20 nm from the surface/interface.