Investigation of band alignment variations in CuZnO/ZnO heterostructures: Synchrotron-based valence band spectroscopy

Quantum well-based semiconductor device's applications depend on energy-band alignments at their interfaces. Many studies have been performed but it's still challenging to find companion band alignments for various applications. In this work, pristine ZnO, CuZnO, and CuZnO/ZnO heterointerfaces with different Cu concentrations were deposited by pulsed laser deposition to demonstrate variation in band offset between CuZnO and ZnO hetero-interface. Valence band spectroscopic studies were performed with synchrotron radiation based high energy X-ray photo-emission spectroscopy (HXPES) to obtain valence band maxima (VBM). The structural and optical characterization of these films were performed using Gi-XRD and UV–Vis spectroscopy. The optical band gap change in ZnO was observed from 3.25 to 2.99 eV with 7 wt% Cu doping. The energy band diagram of CuZnO/ZnO on Zn and Cu levels presents the type-II band alignment. Valence band offset between CuZnO/ZnO interfaces for Zn level was observed at 0.8, 1.7, and 2.27 eV and for Cu level at 0.31, 1.29 and 2.0 eV for 3 wt%, 5 wt%, and 7 wt% doping concentrations, respectively. Similarly, the conduction band offset for Zn level was observed at −0.26, −1.63, −1.8 eV and for Cu level at −0.62, −1.22, −0.9 eV respectively for 3 wt%, 5 wt%, and 7 wt% doping concentrations.