Longitudinal photoconductivity in metal-amorphous silicon-metal structures

Longitudinal photoconductivity has been examined for Pt-α-Si∶H-Ni structures (with the light propagating along the field), with forward bias applied to the structure. There is a difference from transverse photoconductivity, where recombination is important, in that the longitudinal conductivity spectra are determined by generation and drift, where the carriers generated at various depths contribute unequally. The longitudinal-conduction spectra have been calculated for the following cases: 1) constant field in a uniform structure, 2) inhomogeneous field due to change in conductivity on illumination, and 3) inhomogeneous field due to doping or a potential barrier. The comparison with experiment indicates that the last case applies for Pt-α-Si:H structures. The longitudinal conductivity provides information on the electrical homogeneity in wafers and films and on the field distribution.