MICROWAVE MODULATED PHOTOLUMINESCENCE USED TO MEASURE SURFACE RECOMBINATION VELOCITIES

Microwave modulated photoluminescence (MMPL) is a characterization tec hnique in which a semiconducting sample is subjected to continuous opt ical pumping and chopped microwave electric fields. The signal normall y detected in an MMPL experiment is the change in the photoluminescenc e (PL) spectrum due to the presence of the microwave electric field, w hich increases the kinetic energy of the free carriers. We have previo usly correlated the quenching of the PL signal, as induced by the micr owaves, with nonradiative recombination at a surface/interface of the photoexcited volume. In this work, we determine quantitatively surface recombination velocities through a combined measurement of microwave induced changes in photoconductivity and in FL. From the change in the photoconductivity we infer a change in the diffusion constant of free carriers in the material. The change in diffusion constant, along wit h the change in luminescent intensity, uniquely determines the surface recombination velocity of the layer. Results for GaAs layers with bar e surfaces are presented and the potential usefulness of the technique to other material systems, including the measurement of properties of buried interfaces, is discussed. (C) 1998 American Vacuum Society.