Structural, electronic structure, and band alignment properties at epitaxial NiO/Al_2O_3 heterojunction evaluated from synchrotron based X-ray techniques

摘要

The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al_2O_3 heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al_2O_3 substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al_2O_3 substrate. Surface related feature in Ni 2p_(3/2) core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al_2O_3 substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al_2O_3 layers. A type-I band alignment at NiO and A1_2O_3 heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based light emitting devices.