Direct Optical Observation of Band-Edge Excitons, Band Gap, and Fermi Level in Degenerate Semiconducting Oxide Nanowires In2O3

Abstract

Direct optical evidence of Burstein–Moss shift (BMS) in conduction band of cubic c-In2O3 nanowires is reported herein. The optical property of degenerate semiconducting oxide c-In2O3 has been investigated by thermoreflectance (TR) spectroscopy. Low-temperature TR spectra clearly show a series of band-edge excitons for c-In2O3. The threshold energy for the exciton series was determined. One transition feature of direct gap caused by BMS was detected in all TR spectra from 20 to 300 K. The Femi-level (EF) energy above conduction-band edge (EC) is determined to be EF – EC ≈ 92 meV. The energy value causes a calculated electron density of ∼2.1 × 1019 cm–3. The direct gap of c-In2O3 with BMS is 3.43 eV at 300 K. Free exciton, bound exciton complexes, donor–acceptor pair transition, and defect emissions have been evaluated by photoluminescence (PL) measurements from 10 to 300 K. Photoresistivity change (i.e., 5.71 × 10–2 → 4.85 × 10–2 Ω-cm) under the illumination of halogen lamp (5 mW·cm–2) for c-In2O3 thin-film nanorods was detected. The experimental results show In2O3 nanocrystals an appropriate candidate applied not only for light-emitting devices but also for photoelectric-conversion cells.