Misfit epitaxial strain manipulated transport properties in cubic In2O3 hetero-epilayers

In this Letter, we report on the evolution of electronic properties governed by epitaxial misfit strain in cubic In2O3 epilayers grown on sapphire. At elevated growth temperature, the competition between the film/substrate lattice mismatch and the thermal expansion mismatch alters the macroscopic biaxial strain from compressive to tensile. Simultaneously, the electron concentration is tuned from degeneration to non-degeneration density below the Mott criterion. The observed surface electron accumulation and metal-insulator transition result from the oxygen deficiency formed at low growth temperature, while high-temperature epitaxy is favorable to achieve remarkably enhanced mobility. The effective strain-property coupling suggests that the improved oxygen stoichiometry and the Fermi level movement controlled by the biaxial strains are responsible for the Mott transition. The strain-mediated reduction of the electron effective mass contributes to the enhanced intrinsic mobility in tensile-strained In2O3 epilayers. These results highlight that strain engineering is an effective stimulus to manipulate the transport properties of oxide semiconductors with improved performance and unexpected functionalities.