Impact Ionization of Filled Traps in Cadmium Sulfide

Abstract

Pulse measurements have been made of space‐charge limited currents in thin layers of insulating CdS. These were prepared by controlled diffusion of a compensator into conducting n‐type single crystals. Trapping centers were found at 0.4 eV below the conduction band in concentrations around 10¹⁵ cm⁻³ and at 0.6 eV in concentrations around 10¹⁴ cm⁻³. As the electric field was increased above 10⁴ V/cm there was a change in the shape of the current transients. This effect was studied in detail and is attributed to impact ionization of carriers trapped in the 0.6 eV center.