ELECTROREFLECTANCE MODELING OF LOW-FIELD DIELECTRIC CONTRIBUTIONS REQUIRING A BOLTZMANN MODEL OF CARRIER DENSITY

Electroreflectance spectroscopy is a useful diagnostic tool for potent ial and field distribution in semiconductors, and spectra from experim ents performed on samples taken from highly doped (near-degenerate) wa fers of III-V materials have been compared with theory. Satisfactory m odelling has been achieved using recent advances in the understanding of the Moss-Burstein (band-filling) effect, and the accurate modelling of bandgap narrowing and other heavy doping properties is also demons trated. The Moss-Burstein effect makes its principal contribution to t he dielectric function in the low-field region, as does that of excito nic absorption, and both effects are shown to require special computat ional considerations with respect to the electric field profile. When a Boltzmann carrier concentration (rather than a Schottky depletion) m odel is used, the calculated result for the Moss-Burstein effect rapid ly converges to the correct lineshape. The use of the Schottky depleti on model is shown to result in much slower convergence to a signal of much smaller magnitude, and a simple excitonic calculation shows the s ame tendencies, clearly demonstrating the importance of a correct fiel d profile model.