Optical and Electronic Properties of Doped $p$-type CuI: Explanation of Transparent Conductivity from First Principles

TL;DR

This study uses first principles calculations to analyze the electronic and optical properties of doped CuI, explaining its transparent conductivity and potential for improvement through better sample quality.

Contribution

It provides a detailed first-principles explanation of CuI's transparent conductivity and the effects of heavy p-type doping on its electronic structure and optical properties.

Findings

Absence of strong visible interband transitions explains transparency.

Valence band maximum states are dispersive due to antibonding Cu d - I p character.

Dielectric constant of 6.3 reduces impurity scattering, indicating potential for improved conductivity.

Abstract

We report properties of the reported transparent conductor CuI, including the effect of heavy $p$-type doping. The results, based on first principles calculations, include analysis of the electronic structure and calculations of optical and dielectric properties. We find that the origin of the favorable transparent conducting behavior lies in the absence in the visible of strong interband transitions between deeper valence bands and states at the valence band maximum that become empty with $p$-type doping. Instead, strong interband transitions to the valence band maximum are concentrated in the infrared with energies below 1.3 eV. This is contrast to the valence bands of many wide band gap materials. Turning to the mobility we find that the states at the valence band maximum are relatively dispersive. This originates from their antibonding Cu $d$ - I $p$ character. We find a modest enhancement of the Born effective charges relative to nominal values, leading to a dielectric constant $\varepsilon(0)$=6.3. This is sufficiently large to reduce ionized impurity scattering, leading to the expectation that the properties of CuI can be still can be significantly improved through sample quality.