We demonstrate that metal oxides exhibit the same relationship between lattice strain and electronic band gap as nonpolar semiconductors. Epitaxial growth of ultrathin [111]-oriented single-crystal indium-oxide films on a mismatched Y-stabilized zirconia substrate reveals a net band-gap decrease, which is dissipated as the film thickness is increased and the epitaxial strain is relieved. Calculation of the band-gap deformation of In 2 O 3 , using a hybrid density functional, confirms that,

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... the uniaxial lattice contraction along [111] results in a band-gap increase due to a raise of the conduction band, the lattice expansion in the (111) plane caused by the substrate mismatch compensates, resulting in a net band-gap decrease. These results have direct implications for tuning the band gaps and transport properties of oxides for application in optoelectronic devices.