Time dependent electrical resistance of Bi 2(Te 0.4Se 0.6) 3 thin films in vacuum and on exposure to atmosphere

Abstract

Thin films of different thicknesses have been vacuum (2×10 −5 torr) deposited by the flash evaporation technique onto glass plates held at room temperature. In situ measurement of electrical resistance in vacuum (2×10 −5 torr) as a function of time was carried out until the resistance stabilized. Then, on exposure to air by controlled admittance of air into the vacuum chamber, it was found that the resistance of the films increased as pressure increased. After air was admitted up to atmospheric pressure, the resistance was also found to increase as a function of time in the atmosphere. Also, it was observed that the resistance of the film during re-evacuation does not retrace the previous path during the exposure of the films and thus the resistance variation is not reversible. The variation of resistance taking place in the films in vacuum with time is attributed to the coalescence process. The agglomeration rates for the films of different thicknesses were obtained from the linear behavior of ln( R/ R 0) vs time plot. The resistance variation of the films during the exposure to air is attributed to oxygen adsorption. It was found that the annealed films are less influenced by the exposure compared to the as-grown films. Adsorption of oxygen takes place on the external and internal surfaces of the films. The films were found to be ESR active. Structural analysis was carried out using the XRD and TEM techniques.