Point defects: key issues for II-oxides wide-bandgap semiconductors development

Abstract

II-oxides wide-bandgap semiconductor, including the beryllium oxide (BeO), magnesium oxide (MgO), zinc oxide (ZnO), have large exciton binding energy (ZnO 60 meV, MgO 80 meV), high optical gain (ZnO 300 cm<sup>–1</sup>) and wide tunable band gap (3.37 eV ZnO, MgO 7.8 eV, BeO 10.6 eV), which are the advantages of achieving low-threshold laser devices in the ultraviolet wavelength. It is also one of the important candidates to replace the traditional gas arc lamp (such as mercury lamp, deuterium lamp, excimer lamp, xenon lamp etc.) as the source of deep ultraviolet and even vacuum ultraviolet. Although, during the past decades, the ZnO-based pn homojunction devices have made great progress in the near-UV electroluminescence, but as the band gap broadens, the acceptor (or donor) ionization energy becomes higher (On the order of hundreds meV), which causing the room temperature equivalent thermal energy (26 meV) cannot make the impurities ionizing effectively. In addition, the self-compensation effect in the doping process further weakens the carrier yield. These above drawbacks have become the bottleneck that hinders II-oxides wide-bandgap semiconductor from achieving ultraviolet laser devices and expanding to shorter wavelengths, and are also a common problem faced by other wide-bandgap semiconductor materials. The regulation of the electrical and luminescent properties of materials often depends on the control of critical defect states. The rich point defects and their combination types make the II-oxides wide-bandgap semiconductors an important platform for studying defect physics. For the identification and characterization of specific point defects, it is expected to discover and further construct shallower defect states, which will provide a basis for the regulation of electrical performance. In this paper, recent research results of II-oxides wide-bandgap semiconductors will be described from three aspects: high-quality epitaxial growth, impurity and point defects, p-type doping and ultraviolet electroluminescence. Through the overview of related research works, II-oxides wide-bandgap semiconductors are clarified as deep ultraviolet light sources materials. Meanwhile, indicates that the key to the regulation of electrical performance in the future lies in the regulation of point defects.