Photoellipsometry determination of surface Fermi level in GaAs (100)

Abstract

Photoellipsometry, a new contactless optical method, is presented. Related to photoreflectance, this method utilizes spectroscopic ellipsometry with the addition of a laser pump beam directed at nearly normal incidence onto the sample surface, where photoexcited electron-hole pairs modify the built-in electric field as a result of the photovoltaic effect. The field-induced changes in the real and imaginary parts of the complex pseudodielectric function can be directly measured, and analyzed in terms of the pump beam power density or the probe beam photon energy to determine parameters, such as surface Fermi level, built-in field strength, depletion depth, broadening, critical point energies, etc., of a semiconductor under study. Demonstration of this method was made with two n-type GaAs (100) substrates, where the measurements were taken in room air near the band-gap E0 region, for determination of surface Fermi level.