High-field effects in photoconducting cadmium sulphide

High-field characteristics of the photocurrent in CdS are studied by the use of pulse techniques and blocking electrodes. This method enables the determination of surface recombination velocities and bulk trapping times for both electrons and holes. Under special surface conditions, the measurements yield direct information on the electron transport properties at high fields. Of particular interest is the conclusion that the electron drift velocity is linear up to a field of at least 8 × 104Vcm role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{8 × 10}{}^4\text{V}\text{cm}$$\text{8 × 10}{}^4\text{V}\text{cm}$, at which field it attains the value of $̃ role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{\$}\text{̃}$$\text{\$}\text{̃}$10⁷cmsec role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{cm}\text{sec}$$\text{cm}\text{sec}$. The implications of this result in terms of the energy dissipation mechanism in CdS are briefly discussed. The technique described can also be applied to low-resistivity semiconductors.