Electronic structures and unusually robust bandgap in an ultrahigh-mobility layered oxide semiconductor, BiOSe.

Semiconductors are essential materials that affect our everyday life in the modern world. Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices. We investigate the electronic structures of a new layered air-stable oxide semiconductor, BiOSe, with ultrahigh mobility (~2.8 × 10 cm/V⋅s at 2.0 K) and moderate bandgap (~0.8 eV). Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of BiOSe with key parameters (for example, effective mass, Fermi velocity, and bandgap). The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes BiOSe an ideal semiconductor for future electronic applications. In addition, the structural compatibility between BiOSe and interesting perovskite oxides (for example, cuprate high-transition temperature superconductors and commonly used substrate material SrTiO) further makes heterostructures between BiOSe and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers.