Steady-state photocarrier grating technique for the minority-carrier characterisation of thin-film semiconductors

The steady-state photocarrier grating technique allows the determination of the ambipolar diffusion length in low-mobility semiconductors and provides access to the minority-carrier properties in terms of the mobility-lifetime product. The technique probes the excess carrier distribution under the presence of a sinusoidally modulated photogeneration rate which is achieved by the superposition of two coherent laser beams. The relatively simple technique has been established in many laboratories and has been successfully applied to a variety of thin-film semiconductors. The basic theory of the method, experimental set-ups, variants of the experimental realisation in terms of the grating-period or the electric-field variation and some of the various applications of the steady-state photocarrier grating method on thin-film silicon, chalcopyrite and other semiconductors are presented and reviewed in this contribution. Worthwhile information can be obtained on the recombination and the density-of-states in the band-gap of the semiconductor from experiments with the steady-state photocarrier grating method in combination with dark- and photoconductivity measurements.