Tailoring light holes in $\beta$-$Ga_{2}O_{3}$ via Anion-Anion Antibonding Coupling

TL;DR

This paper uncovers the role of anion-anion antibonding coupling in causing heavy hole effective masses in $eta$-$Ga_{2}O_{3}$ and proposes strain engineering to achieve lighter, more mobile holes, enhancing the material's electronic properties.

Contribution

It introduces a design principle to manipulate AAAC effects via strain, enabling the tuning of hole effective masses and reducing self-trapped hole formation in $eta$-$Ga_{2}O_{3}$.

Findings

Strain reduces hole effective mass from 4.77 to 0.38 $m_0$.

Tensile strain decreases self-trapped hole formation energy.

Light holes exhibit significant anisotropy, enabling potential 2D transport.

Abstract

A significant limitation of wide-bandgap materials is their low hole mobility related to localized holes with heavy effective masses ($m_h^*$). We identify in low-symmetric wide-bandgap compounds an anion-anion antibonding coupling (AAAC) effect as the intrinsic factor behind hole localization, which explains the extremely heavy $m_h^*$ and self-trapped hole (STH) formation observed in gallium oxide ($\beta$-$Ga_{2}O_{3}$). We propose a design principle for achieving light holes by manipulating AAAC, demonstrating that specific strain conditions can reduce $m_h^*$ in $\beta$-$Ga_{2}O_{3}$ from 4.77 $m_0$ to 0.38 $m_0$, making it comparable to the electron mass (0.28 $m_0$), while also slightly suppresses the formation of self-trapped holes, evidenced by the reduction in the formation energy of hole polarons from -0.57 eV to -0.45 eV under tensile strain. The light holes show significant anisotropy, potentially enabling two-dimensional transport in bulk material. This study provides a fundamental understanding of hole mass enhancement and STH formation in novel wide-bandgap materials and suggest new pathways for engineering hole mobilities.