3 - Carrier Transport Processes in Amorphous Solids

Abstract

For many years, amorphous semiconductors were not considered suitable as photovoltaic cell materials due to the difficulty experienced in doping such materials to produce the necessary p–n junctions. Eventually, the most familiar application of amorphous semiconductors came to be in the field of replication of printed matter. The xerography process, upon which many modern photocopiers are based, involves the ability of an electrostatically charged plate of amorphous chalcogenide (or similar material) to discharge under illumination. Residual charging of illuminated areas is employed in the transfer of “ink” onto the duplicator paper. Naturally, the mobility of photoinduced carriers in the amorphous semiconductor photoreceptor is of central importance in the validity of the process, and considerable commercial effort has been (and is being) devoted to the study of transport in disordered materials suitable for the process. A second major application of amorphous semiconductors, of comparatively recent emergence, concerns the conversion of solar energy into electrical power.