Dependence of the spectra of charge carriers on the concentration of defects in silver telluride

A change in the band gap as a function of the concentration of electrically active defects in silver telluride has been considered. It has been found that the electronegative and electropositive defects lead to an increase and a decrease in the band gap $\varepsilon_{g_0}$, respectively. It has been revealed that, in Ag$_2$Te with Te concentrations of higher than or equal to 0.75 at%, the band gap $\varepsilon_{g_0}$ has an unusually low value ($\sim$ 0.008 eV). In the case where the band gap is characterized by the temperature dependence $\varepsilon_g$ = (0.008 – 7 $\cdot$ 10$^{-5}$T) eV, at $T >$ 100 K, there is a gapless state. Owing to the changes in the concentration of electrically active defects, silver telluride can exhibit $n$- and $p$-type conductivities, unlike other silver chalcogenides (Ag$_2$S and Ag$_2$Se).