Conductivity of layers of a chalcogenide glassy semiconductor Ge$_2$Sb$_2$Te$_5$ in high electric fields

Effect of high electric fields on the conductivity of 0.5–1-$\mu$m-thick layers of a chalcogenide glassy semiconductor with a composition Ge$_2$Sb$_2$Te$_5$, used in phase memory cells, has been studied. It was found that two dependences are observed in high fields: dependence of the current $I$ on the voltage $U$, of the type $I\propto U^n$, with the exponent $(n\approx 2)$ related to space-charge-limited currents, and a dependence of the conductivity $\sigma$ on the field strength $F$ of the type $\sigma=\sigma_0\exp(F/F_0)$ (where $F_0$ = 6 $\times$ 10$^4$ V cm$^{-1}$), caused by ionization of localized states. A mobility of 10$^{-3}$–10$^{-2}$ cm$^2$/V$^{-1}$ s$^{-1}$ was determined from the space-charge-limited currents.