Investigation of Hole Dopability in Oxygen $2p$-Dominated Bands

TL;DR

This study systematically evaluates 845 oxides to understand the challenges of hole doping in O-2p dominated bands, identifying CaCdO$_2$ as a rare promising candidate and confirming the difficulty of hole doping in such materials.

Contribution

The paper provides a comprehensive high-throughput screening of oxides, revealing the intrinsic difficulty of hole doping in O-2p bands and identifying CaCdO$_2$ as a unique promising example.

Findings

Hole doping in O-2p bands is generally very difficult.

CaCdO$_2$ is identified as a promising hole-doped oxide.

Traditional VBM-raising strategies remain effective.

Abstract

The development of $p$-type oxide semiconductors remains impeded by the inherently low-lying valence-band maximum (VBM) dominated by O-2$p$ states. A prevailing approach to mitigate this limitation is to elevate the VBM by introducing cation states that hybridize with O-2$p$ orbitals or lie energetically above the O-2$p$ level. Nevertheless, the $p$-type oxides reported to date exhibit limited hole mobilities. To expand the search space, it is essential to accurately understand the intrinsic difficulty of introducing holes into O-2$p$-dominated bands. Accordingly, we evaluated 845 oxides to identify those in which holes can be doped into O-2$p$-dominated bands. Our high-throughput screening revealed CaCdO$_2$ as the only promising exemplar, in which the VBM is slightly hybridized with deep-lying Cd-3$d$ states. Our screening suggests that hole doping into O-2$p$-dominated bands is extremely difficult and thus reinforces the effectiveness of the traditional ``VBM-raising strategy.''