Steady-state photocarrier grating method of determining electronic states parameters in amorphous semiconductors

The steady-state photocarrier grating (SSPG) technique is usually used for determining the diffusion length of carriers in amorphous semiconductors. 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. A figure of merit of these materials is a continuous distribution of electronic states over a so-called mobility gap. In the present paper the influence of an energetic distribution of electronic states on results of SSPG measurements is analyzed. Simultaneously, the influence of a spatial distribution of photogenerated carriers over semiconductor thickness is taken into account. Fitting of the angular dependence of the results of SSPG measurements with appropriate theoretical formulae allows the determination of energy levels and densities of acceptor and donor-like states in the investigated a-Si:H.