Electric-field-induced Raman scattering: Resonance, temperature, and screening effects

A comprehensive, experimental characterization of electric-field-induced Raman scattering (EFIRS), a method to probe electric fields within a semiconductor depletion region, is given. Resonance effects, screening of the depletion region by photoexcited carriers, and the influence of temperature on the Raman signal of the symmetry-forbidden, electric-field-dependent LO phonon are discussed for the case of cleaved n-type GaAs surfaces. By comparing results from biased Schottky devices with those from adsorbate-covered surfaces, which were cleaved in ultrahigh vacuum, it is shown that the theoretically expected linear relation between the LO-phonon Raman signal and the Schottky-barrier height holds for the whole range of adsorbate-related potential barriers. In extreme resonance, higher-order effects can affect this relation drastically. However, choosing appropriate power densities of the exciting laser source leads to a partial screening of the space-charge layer by photoexcited carriers, which strongly attenuates these nonlinear effects. Hence a relatively simple calibration of the Raman signals in terms of absolute barrier heights becomes possible by using well-established Schottky-barrier heights as a calibration standard.