奈米材料與薄膜的光學異向性

Abstract

本論文首先探討了張應力對於m面氧化鋅光學異向性的影響。從光激發螢光光譜，我們發現非極化面中的m面氧化鋅的放光異向性僅有10%的極化度，因此我們利用變溫、變極化方向光激發螢光光譜，探討低放光異向性的原因。我們發現在受到張應力的m面氧化鋅中，其極化方向為[0001]的價帶次能帶上升至極化方向為[11-20]的價帶次能帶並與之重疊，因此導致了此非極化面氧化鋅的低放光異向性。建立於此發現，未來再利用鑭鋁酸或鍶鈦酸成長非極化面氧化鋅時，需特別注意其應力對於我們希望得到的具有放光光學異向性的影響。 接著，我們利用 鍶鈦酸作為緩衝層，將非極化面中的a面氧化鋅成長於(001)矽基板上，我們成功的藉由調變基板溫度和氧壓，控制了氧化鋅中不同晶面方向的成長，同時也控制了表面粗糙的程度。此技術在未來可以被用在在矽基板上成長非極化面氧化鋅相關光學元件或是利用其作為緩衝層成長氮化鎵元件於矽基板上。 最後，我們藉由硫化鋅奈米腰帶上極強的表面聲子訊號，研究了表面聲子在拉曼散射中的選擇律。由變極化方向的拉曼光譜，我們發現表面聲子的選擇律異於其對應硫化鋅完美晶體中的聲子，我們認為表面上移動對稱性的異向性破壞，是為此選擇律被打破的主要原因。

Firstly, in order to investigated the optical anisotropy of tensile-strained m-plane ZnO film grown on (112)LaAlO3, temperature and polarization dependent photoluminescence (PL) measurements were performed. The near band edge emission of this non-polar ZnO film shows abnormal low polarization degree (ρ=10%) in PL spectra. To further investigate this characteristic, we studied on the temperature dependency of polarization degree to clarify the origins of different emission peaks. We found that in tensile-strained m-plane ZnO, the [0001] polarized subband upper-shifts and overlaps with the [11-20] polarized subband, causing the abnormal low polarization degree. Secondly, we demonstrated the controlled-growth of non-polar a-plane ZnO on (001)Si substrate by using (001)SrTiO3 as buffer layer. Preferential growth of a-plane ZnO is observed for low substrate temperature and high oxygen pressure. The relation between growth condition and surface roughness of the film is investigated and found to closely relate to the existence of c-plane ZnO. This study offers a promising scheme for controlled growth of non-polar a-plane ZnO on (001)Si and is applicable for further application of ZnO itself or for GaN on (001) Si by using this non-polar ZnO film as buffer layer. High quality ZnS nanobelts (NBs) have been grown by chemical vapor deposition. Finally, on ZnS NBs, we observed strong surface optical (SO) phonon signal and attributed it to the high aspect ratio of ZnS NBs. The selection rule of SO phonon mode was investigated by polarization dependent Raman spectrum performed on single ZnS NB. The selection rule of SO phonon mode is different from the corresponding E1/A1 phonon modes and we ascribed the breakdown of selection rule to the anisotropic translational symmetry breaking on surface.