Switching phenomenon and optical properties of Se85Te10Bi5 films

Se85Te10Bi5 films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se85Te10Bi5 films were amorphous. Electrical conduction activation energy (ΔEσ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se85Te10Bi5 films reveals that it is typical for a memory switch. The switching voltage Vth increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of Vth is found to be 0.325 eV. The switching phenomenon in amorphous Se85Te10Bi5 films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se85Te10Bi5 films. Allowed non-direct transitions with an optical energy gap (Egopt) of 1.33 eV have been obtained. ΔEσ is almost half the obtained value of Egopt, which suggested band to band conduction as indicated by Davis and Mott.