Band Alignment and Enhanced Interfacial Conductivity Manipulated by Polarization in a Surfactant-Mediated Grown κ-Ga₂O₃/In₂O₃ Heterostructure

Abstract

Integration of intriguing ferroelectric κ-Ga2O3 on other oxide semiconductors opens an exciting avenue to invoke emergent transport phenomena and enable rational design of advanced device architectures, whereas the fundamental growth dynamics and physical properties of metastable κ-Ga2O3 are still far unexplored. In this work, we report on the heterostructure construction of single crystalline metastable orthorhombic κ-Ga2O3 epilayers and cubic In2O3(111) by means of laser molecular beam epitaxy. Elements of Sn and In are found to segregate to the growth surface and serve as surfactants to reduce the total surface energy and diffusion barrier of oxygen adatoms, hence producing Ga-rich conditions on the growth front, which in turn facilitates the stabilization of κ-phase Ga2O3. Depth-profiled X-ray photoemission spectral (XPS) analysis identified a type-I band alignment with a conduction band offset (CBO) of 0.45 eV and a valence band offset (VBO) of −1.15 eV for a κ-Ga2O3/In2O3 heterostructure. Determined by the analysis of Hall results with a double-layer model, a two-dimensional electron gas (2DEG) with a sheet carrier concentration of 1.2 × 1014 cm–2 and an enhanced mobility of 192 cm2/(V s) is confined at the heterostructure interface. The self-consistent Poisson–Schrödinger calculations indicate that the enhanced interfacial conductivity is a result of the combination of polarization manipulation and band discontinuity, well-supported by the characteristics of piezoelectric force microscopy and depth-profiled XPS. Integrating κ-Ga2O3 on other hexagonal polar semiconductors may open a possibility to manipulate the interfacial conductivity through polarization engineering and deliver advanced devices with multiple functionalities.