Accurate methods for simulating electroreflectance and photoreflectance spectra of GaAs

Various methods have been used up to now in order to simulate the effects of inhomogeneous electric fields on the modulation spectra of semiconductors. Some methods involve partitioning a layer with a continuously varying field into a series of discrete steps. We show that in the case of a wide space-charge region, solving the resulting set of reflectance equations directly can give misleading results under some conditions because of subtle numerical problems. However, a WKB approach exists that avoids these problems and can be used for GaAs under essentially all conditions. Our simulations lend support to an excitonic mechanism for spectral]] rotation" in photoreflectance of GaAs even at room temperature.