The optical parameters and memory switching of amorphous Se70Te15Bi15 thin films
Films of Se70Te15Bi15 were deposited at room temperature, using thermal evaporation on the glass and pyrographite substrates. The X-ray diffraction pattern confirmed that Se70Te15Bi15 films have an amorphous nature. Optical properties of a-Se70Te15Bi15 films were characterized by using spectrophotometric measurements of transmittance and reflectance in the spectral range (400-2500 nm). The refractive index dispersion curve shows an anomalous dispersion in the absorption region and a normal one in the transmitted region.Analysis of the dependence of absorption coefficient iÂÂÂi in the photon energy reveals allowed indirect transitions with energy gap iÂÂÂ»1.72eV.Optical dispersion parameters according toWemple andDidomenco model were determined. The temperature dependence of the electrical resistance shows parallel straight lines, which indicate single activation energy iÂÂÂÂÂÂEiÂÂÂ³ independent on the filmthickness. Study of static and dynamic current voltage (IÂÂÂÂV) characteristics for a-Se70Te15Bi15 films reveals amemory switch. The mean value of switching voltage Vth increases with increasing the film thickness and decreases with increasing temperature. The value of switching voltage activation energy a was calculated. The calculated ratio iÂÂÂ¥iÂÂÂ¯iÂÂÂÂÂÂEiÂÂÂ³ = 0.54 is nearly to be 0.5, obtained theoretically on the basis of electrothermalmodel. Therefore, the switching phenomenonin a-Se70Te15Bi15 films can be explained according to a physical model based on the electrothermal breakdown theory.