Impact Ionization of Filled Traps in Cadmium Sulfide

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.