Interface Formed via Spontaneous Phase Transition from α- to κ-Ga₂O₃

In this work, we investigated the heterointerface formed between metastable α-Ga 2 O 3 (corundum) and κ-Ga 2 O 3 (orthorhombic). When κ-Ga 2 O 3 was grow on c-plane sapphire at temperatures above 570 °C via mist chemical vapor deposition, α-Ga 2 O 3 initially formed, followed by a spontaneous phase transition from α- to κ-Ga 2 O 3, resulting in an atomically abrupt interface. Despite this abrupt interface, the process was uncontrolled, leading to an uneven interface on a micrometer scale. To address this, the growth process was optimized, identifying strain and temperature as the key control parameters to achieve a uniform and atomically abrupt interface. The band offset at the κ-/α-Ga 2 O 3 interface was analyzed using X-ray photoelectron spectroscopy. The results revealed a type-II band alignment, with the valence and conduction bands of κ-Ga 2 O 3 positioned approximately 1.00 and 0.80 eV higher, respectively, than those of α-Ga 2 O 3 . This was further corroborated by density functional theory calculations. The observed band offset at the pristine κ-/α-Ga 2 O 3 interface holds promise for advanced device designs, offering potential applications in future electronic and optoelectronic technologies.