Band bending independent of surface passivation in ZnO/CdS/Cu(In,Ga)(S,Se)2 heterojunctions and Cr/Cu(In,Ga)(S,Se)2 Schottky contacts

Abstract

We have employed admittance spectroscopy and deep-level transient spectroscopy in order to investigate the electronic properties of $\mathrm{ZnO/CdS/Cu}(\mathrm{In,Ga}\mathrm{)(}\mathrm{S,Se}{)}_2$ heterojunctions and $\mathrm{Cr/Cu}(\mathrm{In,Ga}\mathrm{)(}\mathrm{S,Se}{)}_2$ Schottky contacts. Our work concentrates on the origin of an energy-distributed defect state commonly found in these systems. The activation energy of the defect state addressed continuously shifts upon air annealing or damp-heat treatment and is a valuable measure of the degree of band bending in $\mathrm{Cu}(\mathrm{In,Ga}\mathrm{)(}\mathrm{S,Se}{)}_2$ -based junctions. We demonstrate that the band bending within the $\mathrm{Cu}(\mathrm{In,Ga}\mathrm{)(}\mathrm{S,Se}{)}_2$ layer, reported in the literature to become minimal after air exposure, returns after the formation of either a Schottky contact or a heterojunction. The earlier phenomenon turns out to be independent of a surface passivation due to the CdS bath deposition.