Role of charged defects in the photoconductivity of Se$_{95}$As$_5$ chalcogenide glassy semiconductor with the EuF$_3$ impurity

The energy spectrum of local states associated with charged defects $D^-$ and $D^+$ playing a significant role in carrier generation and recombination in the chalcogenide glassy semiconductor system Se$_{95}$As$_5$ containing EuF$_3$ impurities is proposed based on the study of the temperature dependence of the dark conductivity and steady-state photoconductivity, current-luminance characteristic, and the spectral distribution of the photocurrent. It is shown that EuF$_3$ impurities nonmonotonically change the concentrations of these states. Low concentrations form chemical compounds with selenium and arsenic due to the chemical activity of the rare-earth element and fluorine ions, which result in a decrease in the concentration of initial intrinsic defects. High concentrations, according to the charged-defect model, lead to a decrease in the concentration of $D^+$ centers and an increase in the concentration of $D^-$ centers due to the presence of Eu$^{3+}$ ions. Some parameters of the charged-defect model are estimated, in particular the effective correlation energy $U_{\mathrm{eff}}$ (0.6 eV) and the polaron relaxation energy ($W^+$ = 0.4 eV, $W^-$ = 0.45 eV).