First-principles study of band alignments in the p-type hosts BaM2X2 (M = Cu, Ag; X = S, Se)

TL;DR

This study uses density functional theory to analyze the electronic structures and band alignments of BaM2X2 compounds, revealing their potential for p-type doping and implications for transparent semiconductors.

Contribution

It provides detailed first-principles calculations of band alignments and doping propensities in BaCu2X2 and BaAg2X2 compounds, highlighting effects of element substitution.

Findings

Low ionization energies suggest good p-type doping potential.

Replacing Cu with Ag slightly increases ionization energy and electron affinity.

Band gaps can be tuned by substituting Cu with Ag, affecting transparency applications.

Abstract

The electronic structures of four semiconductor compounds BaCu2S2, BaCu2Se2, BaAg2S2, and BaAg2Se2 are studied by density functional theory using both semi-local and hybrid functionals. The ionization energies and electron affinities were determined by aligning the electronic states with the vacuum level by calculating the electrostatic profile within a supercell slab model. The ionization energy and electron affinity of the compounds were calculated using the Heyd-Scuseria-Ernzerhof (HSE) functionals and range from 4.5 to 5.4 eV and 3.1 to 3.4 eV, respectively. The replacement of Cu by Ag slightly increases the ionization energy and electron affinity, while the replacement of S by Se decreases the ionization energy but slightly increases the electron affinity. Overall, the low ionization energies and small electron affinities suggest that these compounds possess good p-type doping propensities. The band gaps are somewhat small to be ideal candidates for transparent semiconducting behavior. The replacement of Cu with Ag in the barium sulfide compounds can increase the band gap from 1.62 eV to 2.01 eV.