STUDY OF CONCENTRATION-DEPENDENT DIELECTRIC-PROPERTIES OF NORMAL-TYPE GAAS USING VARIABLE ANGLE SPECTROSCOPIC ELLIPSOMETRY

The dielectric function epsilon-spectra of Si-doped n-type GaAs crystals at room temperature (296 K) have been determined between 1.53 and 5.01 eV, using variable angle spectroscopic ellipsometry (VASE). Samples with carrier concentrations ranging from 4.6 x 10(17) to 3.3 x 10(18) cm-3 were measured. The effects of surface microscopic roughness, native oxide overlayer and the subsurface damage were mathematically removed with an appropriate multilayer model The GaAs dielectric function spectra were modeled using the sum of seven harmonic oscillators, whose center energies, half-widths and amplitudes were fitting parameters in the multilayer model. It was found that, as the doping level increased, the E1 and E1 + DELTA-1 peak structures near 3 eV in the epsilon-2 spectrum broadened considerably more than the E0' and E2 peak structures near 4.7 eV, while the amplitude of the E1 peak decreased with respect to that of the E1 + DELTA-1 peak. Other effects due to doping were a shift of the epsilon-2 spectrum towards lower energies and a decrease in the amplitude of the E2 peak.