Thermoluminescence in gallium sulfide crystals: an unusual heating rate dependence

Trap centres in gallium sulfide single crystals have been investigated by thermoluminescence measurements in the temperature range of 10-230K. A curve-fitting method was utilized to evaluate the activation energies (52, 200 and 304meV) of the revealed three trap centres. The heating rate dependence and trap distribution of the peaks have been studied using experimental techniques based on various heating rates and various illumination temperatures, respectively. An anomalous heating rate dependence of the high-temperature peak was found by carrying out TL measurements with various heating rates between 0.2 and 1.0K/s. This behaviour was explained on the basis of a semi-localized transition model. Whereas normal heating rate dependence was established for low-temperature peak, that is, the TL intensity of the glow curve decreases and the peak maximum temperature shifts to higher values with increasing the heating rate. Moreover, a quasi-continuous trap distribution with the increase of activation energies from 52 to 90meV, from 200 to 268meV and from 304 to 469meV for the observed three different traps was established employing the various illumination temperatures method.