STUDY OF EXCITONIC PROPETIES OF LOW-DIMENSINAL ZnO

利用激光分子束外延技术成功地生长出了高质量的ZnO外延层，这对于新型紫外半导体激光器的研究具有重要意义。对于激光器结构的制作，在该材料系统中，开发具有比ZnO更大带隙的包覆材料是重要的。采用激光分子束外延成功地实现了Mg在ZnO中的掺杂，掺杂量达到20%，从而提高了ZnO的禁带宽度。在蓝宝石衬底上生长ZnO/MgZnO多量子威尔斯（MQW）结构，观察其载流子限制效应。通过X射线衍射测量以及透射电子显微镜观察证实了尺寸为10 nm量级的周期性结构。在本研究中实现的最小阱宽度为约1 nm。利用低温光致发光（PL）和光致发光激发（PLE）研究了这些结构中的量子化电子态。通过减小阱宽，观察到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相一致。PL峰和PLE峰之间较大的Stokes位移表明定域激子在这些NIQW中起着重要作用，PL测量的温度依赖性也证实了这一点。

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.