Influence of copper on the electronic properties of amorphous chalcogenides

TL;DR

This study investigates how copper alloying alters the electronic structure of amorphous arsenic sulfide, revealing changes in atomic coordination, electron localization, and potential effects on photodarkening.

Contribution

It provides detailed atomic-level insights into copper's role in modifying the electronic properties of amorphous chalcogenides, including configurations and electronic states.

Findings

Copper exists in Cu(I) and Cu(II) states with distinct coordination geometries.

Copper addition increases overcoordinated arsenic and sulfur atoms.

Copper states at the valence band top mask photodarkening effects.

Abstract

We have studied the influence of alloying copper with amorphous arsenic sulfide on the electronic properties of this material. In our computer-generated models, copper is found in two-fold near-linear and four-fold square-planar configurations, which apparently correspond to Cu(I) and Cu(II) oxidation states. The number of overcoordinated atoms, both arsenic and sulfur, grows with increasing concentration of copper. Overcoordinated sulfur is found in trigonal planar configuration, and overcoordinated (four-fold) arsenic is in tetrahedral configuration. Addition of copper suppresses the localization of lone-pair electrons on chalcogen atoms, and localized states at the top of the valence band are due to Cu 3d orbitals. Evidently, these additional Cu states, which are positioned at the same energies as the states due to ([As4]-)-([S_3]+) pairs, are responsible for masking photodarkening in Cu chalcogenides.