The influence of gas adsorption on electrical resistance of thin films of tellurium

Films of tellurium thickness 700 deg A-3000 deg A were prepared onto unheated 7059 glass substrate at 300 deg K and 5x10-5 Torr of vacuum in conventional oil pumped system. A study of change in electrical resistance before and after adsorption of dry air, hydrogen, nitrogen and moisture as a function of pressure has been made. The change in electrical resistance due to adsorption of gases also depends on the film thickness, deposition angle, the time for which adsorption is taking place, the nature and the amount of adsorbed gases. The presence of various adsorbed gases increases the semiconduction currents in tellurium thin films by several orders of magnitude and decreases the activation energy for semiconduction. The increase in conductivity attributed to adsorption in the film producing accepter states in the valence band and effectively increasing the hole concentration. The process is reversible simply by adsorbing the gases. The adsorption of moisture has a marked decrease in resistivity and shows an interesting hysterisis behaviour. (author)