Charge carrier transport in Ge$_{20}$As$_{20}$S$_{60}$ chalcogenide semiconductor films

Charge-carrier transport in Ge$_{20}$As$_{20}$S$_{60}$ films has been studied using the transit time method under low-injection conditions at room temperature. It was found that drift mobilities of electrons and holes in Ge$_{20}$As$_{20}$S$_{60}$ films are close to each other, i.e., $\mu_e\approx\mu_h\approx$ 2 $\cdot$ 10$^{-3}$ cm$^2$V$^{-1}$ s$^{-1}$ at $T$ = 295 K and $F$ = 5 $\times$ 10$^4$ V/cm. It was shown that the time dependence of the photocurrent during carrier drift and the voltage dependence of the drift mobility allowed the use of the concept of anomalous dispersive transport. Experimental data were explained using the model of transport controlled by carrier trapping by localized states with energy distribution near conduction and valence band edges described by the exponential law with a characteristic energy of $\sim$0.05 eV.