Effect of O2 and H2 plasma treatments on the properties of CuInSe2 polycrystalline thin films

Abstract

In this work, the effects of O2 and H2 plasmas on the properties of grain bulk and the grain boundaries in polycrystalline CuInSe2 (CIS) thin films are investigated. The electrical behaviour of such material is dominated by the defects; in particular grain boundaries, which control charge transport and carrier recombination. CuInSe2 thin films obey to two mechanisms of carrier transport, which operate simultaneously: The thermoionic emission through the intergrain barrier at high temperatures, and the "Variable Range Hopping" (VRH) in the forbidden band at low temperatures. Characterization including Conductivity, Impedance and Thermally Stimulated Current (TSC) measurements was done before and after O2 and H2 treatments. Conductivity versus temperature characteristics were studied in the range of 80-400K while Impedance measurements for different frequencies were realized at high temperature. These measurements showed that O2 and H2 plasmas passivate grain boundary defects in p and n type samples, respectively and have doping effects on the bulk grain: p type films are doped p+ by oxygen while n type ones are n+ doped by hydrogen.