Influence of spatial distribution of radiation on steady-state photocarrier grating measurement

The influence of spatial distribution of radiation intensity on results of steady-state photocarrier grating (SSPG) measurements is analyzed. This technique uses the interference pattern obtained over an illuminated sample surface when two coherent radiation beams hit the sample at different angles of incidence. The sample usually consists of a thin semiconductor film on a thick, parallel-sided substrate. In this paper, the interference of radiation internally reflected in the thin film as well as internally reflected in the substrate are taken into consideration. These phenomena evoke complicated spatial distributions of radiation in a sample, and consequently they affect the magnitude of photoconductivity. The value of SSPG response can be even a few times greater than the predicted one for a homogeneous distribution of light over the thickness of a semiconductor film. If one does not take this effect into account, the carrier diffusion lengths estimated with the SSPG technique may vary from those suggested by the measurement.