点缺陷调控:宽禁带Ⅱ族氧化物半导体的机遇与挑战

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

宽禁带Ⅱ族氧化物半导体材料体系,包括氧化铍(BeO)、氧化镁(MgO)、氧化锌(ZnO)及合金,拥有较大的激子结合能(ZnO 60 meV, MgO 80 meV),较高的光学增益(ZnO 300 cm-1)以及较宽的可调带隙(ZnO3.37 eV, MgO 7.8 eV, BeO 10.6 eV),具有实现紫外及深紫外波段低阈值激光器的独特优势,同时也是取代传统气体放电灯(汞灯、氘灯、准分子灯、氙灯)成为深紫外乃至真空紫外光源的重要候选材料之一.虽然经过20余年的研究历程, ZnO基pn同质结近紫外电致发光方向取得了长足进步,但是,随着带隙的展宽,伴随而来的受主(施主)离化能变高(百毫电子伏特量级),使得室温等效热能(26 meV)无法实现对杂质能级上的空穴(电子)有效离化;此外,掺杂过程中存在的自补偿效应也进一步弱化了载流子的产率,以上因素已经成为了阻碍宽禁带Ⅱ族氧化物半导体实现紫外激光器件及向更短波长扩展的瓶颈性问题,同时也是其他宽禁带半导体材料共同面对的难题.对材料电学及发光性能的调控往往取决于对关键缺陷态的识别与控制,丰富的点缺陷及其组合类型,使宽禁带Ⅱ族氧化物半导体成为研究缺陷物理的重要平台.针对特定点缺陷的识别及表征将有望发现并进一步构建能级较浅的缺陷态,为电学性能调控提供基础.本文从高质量外延生长、杂质与点缺陷、p型掺杂及紫外电致发光三个方面阐述Ⅱ族氧化物半导体近期研究结果,通过对相关研究工作的概览,阐明该体系作为深紫外光源材料的独特优势的同时,指明未来针对电学性能调控的关键在于对点缺陷的调控.

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-1)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: highquality 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.