STUDY OF EXCITONIC PROPETIES OF LOW-DIMENSINAL ZnO

利用激光MBE技术成功地生长出了高质量的ZnO外延层，成为新型紫外半导体激光器的研究热点。对于激光结构的制造，开发比ZnO带隙更大的包层材料是该材料体系的重要组成部分。利用激光MBE技术成功地实现了氧化锌中Mg的掺入率高达20%，导致带隙增大。在蓝宝石衬底上生长ZnO/MgZnO的多量子阱结构，观察其载流子约束效应。通过x射线衍射测量和透射电镜观察，确定了尺寸为lOnm级的周期结构。在本研究中获得的最小井宽约为1 nm。用低温光致发光（PL）和光致发光激发（PLE）研究了这些结构中的量子化电子态。通过减小量子阱的宽度，我们观察到了PL发射峰和PLE吸收峰的蓝移，这与基于量子阱结构的计算结果吻合得很好。PL和PLE峰之间的大斯托克位移表明局域激子在这些NIQWs中起着重要作用，这也从PL测量的温度依赖性结果中得到了证实。

High quality epitaxial layers of ZnO were successfully grown by laser MBE, which attracts much attention for new ultra-violet semiconductor lasers. For the fabrications of laser structures, development of cladding materials with larger bandgap than ZnO is important in this material system. Incorporation of Mg into ZnO up to 20% was successfully achieved using laser MBE, resulting in the increase of bandgap. Multi-quantum wells (MQWs) structures of ZnO/MgZnO were grown on sapphire substrates to observe the carrier confinement effects. The periodic structures with the order of lOnm in sizes were confirmed by a x-ray diffraction measurement as well as a transmission electron microscope observation. The minimum well width achieved in this study was about 1 nm. Low temperature photoluminescence(PL) and photoluminescence excitation(PLE) were performed to investigate the quantized electronic states in these structures. Blue shift of PL emission peaks as well as PLE absorption peaks were observed by decreasing the well width, which is in good agreement with the calculations based on quantum well structures. The large stokes shift between PL and PLE peaks exhibits that the localized excitons play an important role in these NIQWs, which was also confirmed from the result of temperature dependence of PL measurement.