Electronic and optical properties of native point defects in CuInS$_2$ and CuGaS$_2$

TL;DR

This study uses advanced hybrid functional calculations to analyze intrinsic defects in CuInS$_2$ and CuGaS$_2$, linking defect levels with optical properties and improving agreement with experimental photoluminescence data.

Contribution

It provides a comprehensive analysis of defect electronic and optical properties in CuInS$_2$ and CuGaS$_2$ using HSE hybrid functional, including the effects of lattice relaxation.

Findings

Charge-transition levels are connected to optical-transition levels.

Lattice relaxation significantly affects emission properties.

Predictions align better with experimental photoluminescence data.

Abstract

We present a detailed study of common intrinsic defects in CuInS$_2$ and CuGaS$_2$ using the Heyd, Scuseria and Ernzerhof (HSE) hybrid functional scheme. The impact of the two HSE parameters, $\alpha$ and $\omega$ on the band gap and compliance with the generalized Koopmans' theorem is investigated. Using the formation energy formalism and calculated thermodynamic charge-transition levels, we assess the electronic properties of the defects and explore the connection of charge-transition levels with optical-transition levels. Calculated Franck-Condon shifts for emission highlight the importance of lattice relaxation for the attribution of defects to luminescence peaks. Our results show that once these effects are included, predictions become closer to photoluminescence measurements available in literature.