7. Photoconductivity in Materials Research

Photoconductivity is the incremental change in the electrical conductivity of a substance upon illumination. Photoconductivity is especially apparent for semiconductors and insulators, which have low conductivity in the dark. Significant information can be derived on the distribution of electronic states in the material and on carrier generation and recombination processes from the dependence of the photoconductivity on factors such as the exciting photon energy, the intensity of the illumination or the ambient temperature. These results can in turn be used to investigate optical absorption coefficients or concentrations and distributions of defects in the material. Methods involving either steady state currents under constant illumination or transient methods involving pulsed excitation can be used to study the electronic density of states as well as the recombination. The transient time-of-flight technique also allows carrier drift mobilities to be determined.