Temperature-dependent enhancement in free-exciton photoluminescence of Zn nanoplates and ZnO hierarchical nanostructures

• Main Authors: Han-Sheng Chou, 周翰昇
• Other Authors: Yuan-Ron Ma
• Format: Others
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/g84d92

碩士 === 國立東華大學 === 物理學系 === 105 === In this study, Zn nanoplates were synthesized using hot-plate metal vapor deposition (HPMVD) technique. The as-synthesized Zn nanoplates are annealed at different temperatures (400,450,500,550 ºC) in presence of oxygen to synthesize ZnO hierarchical nanostructures using quartz tube furnace chemical vapor deposition (TFCVD) technique. The morphology, chemical properties, crystalline structures, and luminescence properties are studied using field-emission scanning electron microscopy (FESEM), energy dispersive spectrometry, (EDS), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), photoluminescence (PL) respectively. We discussed three different photoluminescence mechanisms of Zn (metal), ZnO (semiconductor), and Zn/ZnO (metal-semiconductor concentric). The PL emissions of the metallic Zn is mainly dependent on the electron transitions between the Fermi level (EF) and the 3d band. In case of semiconducting ZnO, the dominant PL emissions are occurred due to the near band edge (NBE) electron transitions. However, the nanostructured Zn/ZnO heterojunctions shows PL emissions due to electron recombination between EF to valence and 3d band as well as NBE transitions. The effect of lowering of temperature to 80 K are studied for three different nanostructures viz. Zn, ZnO, and Zn/ZnO. The temperature-dependent photoluminescence spectra has shown a strong enhancement in free-exciton PL intensity. Moreover, the three structures not only show an enhancement in PL intensity but also exhibits a blue-shift with decreasing temperature. Along with the photoluminescence mechanisms we discussed internal quantum efficiency (IQE). All the results iterate that Zn, ZnO, and Zn/ZnO nanostructures are excellent to use in optoelectronic nanodevices such as light-emitting diodes and laser diodes.