  We have employed admittance spectroscopy and deep-level transient
spectroscopy in order to investigate the electronic properties of
ZnO/CdS/Cu(In,Ga)(S,Se)$_2$ heterojunctions and Cr/Cu(In,Ga)(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
Cu(In,Ga)(S,Se)$_2$-based junctions. We demonstrate that the band bending
within the Cu(In,Ga)(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.
