The high exciton binding energy, radiation hardness and range of achievable bandgaps of wurtzite Zn1‑xMgxO make it suitable for applications including UV filters and detectors.
In this work, energetic film growth methods (high impulse power magnetron sputtering (HiPIMS) and filtered cathodic vacuum arc deposition) have been used to deposit Zn1‑xMgxO with differing Mg fractions (x). Electron microscopy, X-ray absorption spectroscopy (XAS) and electrical/optical measurements have been performed to provide detailed characterisation of the resulting n-type Zn1‑xMgxO films and devices. The optical bandgap of the highly transparent films varied monotonically with x up to the miscibility limit of x ~ 0.32, beyond which a mixed cubic/wurtzite structure formed (observed in the optical characteristics and in XAS).Transmission electron microscopy revealed pseudo epitaxial growth up to a thickness of ~90 nm in the semi-insulating HiPIMS wurzite films. Annealing these at 550°C in forming gas (95% N2, 5%H2), caused reduced compressive stress, increased optical band-gap and dramatically reduced electrical resistivity without detectable phase transformation. After further annealing experiments, the reduced electrical resistivity was attributed in part to the introduction of shallow donors in the form of hydrogen occupying oxygen vacancies.
Finally, prototype visible-blind Schottky UVB detectors have been demonstrated and cross-sectional TEM has been used to determine the interface structure of these devices. This work has shown that energetic deposition is capable of producing low cost, high quality band-gap tuned ZnO-based devices.