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

TL;DR

This study shows that band bending in Cu(In,Ga)(S,Se)$_2$-based heterojunctions and Schottky contacts is unaffected by surface passivation and can be restored after air exposure through contact formation, using admittance and deep-level transient spectroscopy.

Contribution

It reveals that band bending in these heterojunctions is independent of surface passivation, challenging previous assumptions about surface effects.

Findings

Band bending is unaffected by surface passivation.

Band bending can be restored after air exposure.

Defect state activation energy shifts with treatments.

Abstract

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.