Time dependent electrical resistance of Bi-2(Te0.4Se0.6)(3) thin films in vacuum and on exposure to atmosphere

Thin films of different thicknesses have been vacuum (2 X 10(-5) torr) depo sited by the flash evaporation technique onto glass plates held at room tem perature. In situ measurement of electrical resistance in vacuum (2 x 10(-5 ) torr) as a function of time was carried out until the resistance stabiliz ed. Then, on exposure to air by controlled admittance of air into the vacuu m chamber, it was found that the resistance of the films increased as press ure increased. After air was admitted up to atmospheric pressure, the resis tance was also found to increase as a function of time in the atmosphere. A lso, it was observed that the resistance of the film during re-evacuation d oes not retrace the previous path during the exposure of the films and thus the resistance variation is not reversible. The variation of resistance ta king place in the films in vacuum with time is attributed to the coalescenc e process. The agglomeration rates for the films of different thicknesses w ere obtained from the linear behavior of In(R/R-0) vs time plot. The resist ance variation of the films during the exposure to air is attributed to oxy gen adsorption. It was found that the annealed films are less influenced by the exposure compared to the as-grown films. Adsorption of oxygen takes pl ace on the external and internal surfaces of the films. The films were foun d to be ESR active. Structural analysis was carried out using the XRD and T EM techniques. (C) 1998 Elsevier Science Ltd. All rights reserved.