Band alignment of monolayer CaP$_3$, CaAs$_3$, BaAs$_3$ and the role of $p$-$d$ orbital interactions in the formation of conduction band minima

TL;DR

This study investigates the band alignment of monolayer CaP$_3$, CaAs$_3$, and BaAs$_3$ using quasiparticle calculations, revealing type-II heterojunctions and the influence of $p$-$d$ orbital interactions on their electronic properties.

Contribution

It provides the first quasiparticle-level band alignment analysis of these 2D materials, highlighting the role of $p$-$d$ interactions in their conduction band formation.

Findings

All three monolayers form type-II heterojunctions.

Quasiparticle gaps are 2.1 eV (CaP$_3$), 1.8 eV (CaAs$_3$), 1.5 eV (BaAs$_3$).

The indirect gap in BaAs$_3$ is due to strong As $3p$ - Ba $5d$ bonding.

Abstract

Recently, a number of new two-dimensional (2D) materials based on puckered phosphorene and arsenene have been predicted with moderate band gaps, good absorption properties and carrier mobilities superior to transition metal dichalcogenides. For heterojunction applications, it is important to know the relative band alignment of these new 2D materials. We report the band alignment of puckered CaP$_3$, CaAs$_3$ and BaAs$_3$ monolayers at the quasiparticle level of theory (G$_0$W$_0$), calculating band offsets for isolated monolayers according to the electron affinity rule. Our calculations suggest that monolayer CaP$_3$, CaAs$_3$ and BaAs$_3$ all form type-II (staggered) heterojunctions. Their quasiparticle gaps are 2.1 (direct), 1.8 (direct) and 1.5 eV (indirect), respectively. We also examine trends in the electronic structure in the light of chemical bonding analysis. We show that the indirect band gap in monolayer BaAs$_3$ is caused by relatively strong As $3p$ - Ba $5d$ bonding interactions that stabilize the conduction band away from the $\Gamma$ point between $\Gamma$ and $S$.