Thermoelectrical properties and memory switch phenomenon in amorphous Ge46S54 films

Amorphous Ge46S54 films obtained by thermal evaporation in vacuum were investigated. The electrical conductivity and thermoelectric power have been studied as a function of temperature in the range 293–445 K, and the activation energies have been determined for films with thicknesses between 123 and 370 nm. The measurements on d.c. conductivity indicate a single value activation energy of 0.968 eV for the conductivity in the applied temperature range. The sign of thermopower is found to be positive indicating that conduction takes place due to the holes in the valence band. The conduction mechanism is due to the tunnelling of carriers in the localized states in the band edges. It was also found that the investigated samples show a memory effect. The threshold switching voltage was found to increase linearly with film thickness. Moreover, the threshold voltage decreases exponentially with temperature in the range 293–343 K. The switching phenomenon can be satisfactorily explained using the electrothermal model of breakdown.