Switching Effects in Evaporated Arsenic Sulphide Films

Abstract

Thin films of arsenic trisulphide were evaporated from amorphous arsenic sulphide bulk material, by high vacuum evaporation technique on to glass substrates at room temperature. Electrodes used to measure the current (I) voltage (V) characteristics were made of aluminium. The current-voltage characteristics obey the relationI=aVnwhere a is a constant. Value of n ranges from 1 at relatively lower voltages to higher values for higher voltages. At threshold voltage (Vth), the material switches on to a highly conducting state. This change in structure is regenerative in contrast to the nonregenerative breakdown for an insulator; because on increasing the voltage in the on-state, current increases linearly obeying the Ohm's Law and after a critical current value, it suddenly switches back to the initial off-state condition. The threshold voltage (Vth) decreases with increasing the temperature from 300°K to 440°K.The non-linearity in I—V characteristics in the off-state condition corresponds to different types of conduction mechanisms, viz. Schottky emission, Poole-Frenkel emission, space-charge limited currents or tunnelling in potential barriers. All these phenomena indicate the presence of localized states within the band gap.The mechanism of electrical breakdown in these films which depends on temperature for given thickness of films and sample geometry has been discussed.