Effective mass tensor in pristine Ga2O3 polymorphs: Implications for charge transport

Gallium oxide has emerged as a promising ultra-wide-band-gap semiconductor for next-generation high-power electronic and deep-ultraviolet optoelectronic applications. The availability of several crystallographic polymorphs, including the thermodynamically stable β phase and metastable α, κ, and δ phases, provides opportunities to tailor electronic and optical properties through phase engineering. Although electron effective mass tensors have been extensively investigated using density functional theory (DFT), the hole effective masses remain poorly understood owing to their large values and the associated computational challenges. In this work, we revisit the effective mass tensors of the α-, β-, κ-, and δ-Ga 2 O 3 polymorphs using DFT calculations based on the modified Becke–Johnson exchange potential, which provides an improved description of the electronic band structure. The results reveal a pronounced anisotropy of the hole effective masses, particularly in the rhombohedral and orthorhombic phases, where values as large as 50 m 0 and 106 m 0 are obtained along specific crystallographic directions. Such heavy hole masses indicate limited hole transport and strongly anisotropic carrier dynamics. In contrast, the electron effective masses are considerably smaller and less anisotropic, yielding effective masses below 0.4m 0 for all investigated phases. Among the investigated polymorphs, the cubic phase exhibits the lowest average hole effective mass, while the monoclinic phase exhibits the lowest average electron effective mass.