Light, annealing and plasma induced changes on the electrical properties of a-GaSe thin films

摘要

Thin films of GaSe were deposited at room temperature on glass substrate by the physical vapor deposition technique. These films were irradiated with light for 6 hrs at room temperature using heat filtered white light by using a tungsten lamp (1035 lux), annealed at 523 K for 1 hr and irradiated with argon plasma (p∼0.2 mbar, I=20 mA) for 1 hr. Dark conductivity measurements were made on as-deposited and irradiated GaSe thin films in the temperature range 100–370 K in order to identify the conduction mechanism and the effect of different treatments on its electrical properties. The obtained results revealed two distinct regions. The mechanisms of such regions were analyzed. At high temperatures dc conductivity (σ _d) obeys the law ln σ∝1/T, indicating conduction in extended states, and at low temperatures, obeys the law ln σ∝T −1/4, indicating variable-range hopping in localized states near the Fermi level. The density of localized states N(E _F) and various other Mott’s parameters like the degree of disorder (T _o), hopping distance (R) and hopping energy (W) near the Fermi level is calculated before and after different treatments using dc conductivity measurements at low temperatures. Steady-state photo-conductivity measurements were done in the temperature range 303–373 K by using heat filtered white light.