Photoconductivity methods in materials research

Photoconductivity refers to the incremental change upon illumination of the electrical conductivity of a substance. For semiconductors and insulators, where the conductivity in the dark is low, significant changes can be measured. From the dependence of the photoconductivity on factors such as the exciting photon energy, the intensity of the illumination or the ambient temperature, significant information can be derived on the distribution of electronic states in the material and on carrier generation and recombination processes. Those results in turn provide indications about optical absorption coefficients or concentrations and distributions of defects in the materials. Both steady-state currents under constant illumination and 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 further allows the determination of carrier drift mobilities. Photocurrents can also be used to measure interface barriers through internal photoemission or to detect electron spin resonance. (C) 2005 Springer Science + Business Media, Inc.