Carrier Transport and Generation in Orthorhombic Sulphur Crystals by Pulsed X-Rays

A study of the dependence of the carrier mobilities on temperature and crystal thickness in orthorhombic sulphur crystals was performed using 0.4 µsec X-ray pulses in order to avoid surface effect. The saturation of the collected charge at applied fields exceeding 40 kV/cm was found to be due to the so-called “schubweg effect.” At 290°K the values of schubweg per unit field for electrons and holes are estimated at 6×10 -7 and (1-5)×10 -6 cm 2 V -1 , respectively. With the mobility data, the results lead to the lifetimes of 800 µsec for electrons and 66 µsec for holes. The number of carrier pairs generated by X-rays is relatively insensitive to temperature. The energy necessary to create an electron-hole pair lies between 16 and 30 eV. The effect of excitons on carrier generation may be important in uniform excitation by X-rays.