單根氧化鋅奈米線極化光學性質

Abstract

由於微影曝光技術將到物理極限，因此要製作更小的元件必須尋求其他方法。其中以單根奈米線作為根基是一新的方式，由於它屬於一維的結構，因此在電性及光性的傳導上有很好的優勢，而且尺寸可藉由製程進行有效的控制，所以有機會取代原本的元件製作。過往的量測上所得到的性質為多數奈米線的加乘結果，並不能代表單一奈線的基本特性，因此本論文中將從單根奈米線的光學性質進行研究，以利後續的發展。 本實驗的氧化鋅奈米線是運用化學浴沉積法(chemical bath deposition，CBD)的方式成長，長度大約為10μm，再藉由敲擊的方式散佈單根奈米線於矽晶片上，以進行後續的極化光學量測，在本實驗中主要為討論綠色缺陷發光的性質。而光學量測主要分為三個部分：(1)光致激發極化光譜(PL) (2)時間解析光致激發極化光譜(TRPL) (3)拉曼極化光譜。在光致激發極化光譜中可發現發現缺陷發光會沿著奈米線長軸比較強，而光激子(exciton)則相對較弱。而在時間解析光致激發極化光譜中則發現缺陷發光沿著長軸生命週期(lifetime)較短。在第三部份拉曼光譜中，可發現拉曼光譜會隨著不同雷射極化方向的激發而產生晶格震動模式的改變。

Because of the lithography technique approaches the physical limit, it must to elstablish some new process to manufacture the smaller device. There is a new method to make the devices which use the single nanowire as the building blocks. There are two apparent advantages for nanowires. First, nanowires belong to one-demensional structure, so they have better electrical transportation and optical propagation properties. Second, the material size could be adjusted by controlling the parametrs of the process. So there is a great opportunity to replace the lithography process in the future. The basic properties are not all the same between the ensembles and the single nanowire, so in this thesis we focus on the single nanowire optical properties. In our experiment the zinc oxide nanowires are synthesized by chemical bath deposition (CBD) and the diameter is about 10μm. The preparation of the single nanowire specimen is tapping the back of the ensembles substrate and then the wires would be dispersed on the silicon wafer. After that we will measure the polarization optical properties of single nanowire, in this thesis we concentrate on the green defect emission. Optical measurement would be separated into three parts (1) photoluminescence polarization spectrum (PL) (2)time-resolved photoluminescence polarization spectrum (TRPL) (3)Raman polarization spectrum. In the PL spectrum, we find out that the defect emission would be stronger along the long axis and is opposite to the exciton emission. In TRPL spectrum, the lifetime of the defect band would be shorter along the long axis. In the Raman spectrum, the main phonon modes will be changed due to different laser polarization.