Band gap and electronic structure of cubic, rhombohedral, and orthorhombic In2O3 polymorphs: Experiment and theory

Recent studies on In2O3 have revealed a rich phase diagram and have led to the discovery of new In2O3 polymorphs, including the synthesis and ambient recovery of Pbcn In2O3. The electronic properties of this new phase are studied together with other better-known polymorphs (Ia (3) over bar and R (3) over barc) using soft x-ray absorption and emission spectroscopy, directly probing the partial density of states and transition matrix elements. Together with complementary full-potential all-electron density functional theory calculations, this allows important material parameters, such as the electronic band gap and partial density of states, to be elucidated. Excellent agreement between experiment and theory is obtained, with band gaps of 3.2 +/- 0.3, 3.1 +/- 0.3, and 2.9 +/- 0.3 eV determined for the Ia (3) over bar, R (3) over barc, and Pbcn In2O3 polymorphs, respectively. The effective mass of carriers in Pbcn In2O3 is predicted to be 12% less than in the widely used Ia (3) over bar polymorph while having a similar effective optical band gap.