摻雜銦/鎵之氧化鋅奈米結構與光學特性之研究

Abstract

在此篇論文中，探討利用熱蒸鍍法在兩段式溫控真空爐管系統之銦/鎵摻雜氧化鋅奈米結構成長及特性的研究。在本人實驗中成功地在金奈米粒子覆蓋的矽/二氧化矽基板上成長出具有不同銦元素濃度(含量小於1%)的氧化鋅奈米柱以及在不同成長環境下鎵元素含量為1%的氧化鋅薄膜。之後利用掃描電子顯微鏡圖像、穿透式電子顯微鏡圖像、X光繞射圖、能量散佈光譜、四點探針、光激發螢光發光光譜和N&K薄膜測厚儀來分析結構上、成分上、電性以及光性的性質。 在第一部份實驗中，從SEM圖形上發現長度大約為500奈米、直徑範圍介於20至80奈米的銦摻雜氧化鋅奈米柱。並且從掃描式電子顯微鏡圖像及穿透式電子顯微鏡圖像的量測結果中，奈米柱的頂端發現具備催化劑效果之金奈米粒子的存在，而證實奈米柱成長乃經VLS機制。經由XRD的結果得到晶體品質隨著藉EDS量測而得的銦摻雜濃度的增加而降低。在光激發螢光發光光譜中，從奈米柱之近傳導帶發射訊號隨著提昇的銦摻雜濃度產生的藍移以及其強度的削減，分別可藉由Burstein-Moss效應和施子引發的非輻射性復合來解釋。 在第二部份實驗中，從SEM圖形上發現厚度大約為100奈米的鎵摻雜氧化鋅薄膜。在經由氧流量調變實驗中，從掃描式電子顯微鏡圖像中得到薄膜表面形態幾乎相同，但從X光繞射圖得到的晶體品質和和四點探針得到的片電阻值均隨著氧流量的下降而降低。另外隨著成長溫度的提昇，薄膜具有更粗糙的表面形態、更好的晶體品質以及更高的導電率。在光激發螢光光譜中，綠光帶發射訊號強度隨氧流量的減少而增強，除此之外，由於成長溫度的提昇所造成的近傳導帶發射訊號的藍移以及綠光帶訊號強度的降低，可分別以電子載子濃度的提昇和氧缺陷的減少作為解釋。

In this thesis, I study on the growth and characterizations of indium/gallium doped zinc oxide nanostructures in a two-zone temperature controlled vacuum furnace system by using a thermal evaporation method. Zinc oxide nanorods doped with different indium concentration (<1%) and 1% gallium doped zinc oxide thin films prepared at various growth conditions were successfully synthesized on gold nanoparticle coated Si/SiO2 substrates in my experiments. Afterwards, the structural, componential, electrical and optical properties were analyzed by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS), four-point probe, Photoluminescence (PL) and N&K measurement. In the first section of my experiments, indium doped zinc oxide nanorods with about 500 nm in length and 20~80 nm in diameter were found in the SEM images. From the SEM and TEM results, gold nanoparticles which act as catalyst were observed to be located on the top of the nanorods, which testified the nanorods were formed via VLS mechanism. It was found that the crystal quality degraded with the increasing indium doping concentration, examining by the EDS measurement, from the XRD investigation. PL shows the slight blue-shift and the depressed intensity of the near-band-edge (NBE) emission of the nanorods with higher indium doping concentraiotn, which can be explained by Burstein-Moss effect and the formation of donor-induced nonradiative recombination centers, respectively. In the second section, gallium doped zinc oxide thin films with about 100 nm in thickness were found in the SEM images. In the modulation of oxygen flow rate, the surface morphologies of the films were almost the same but the crystal quality and sheet resistance degraded and decreased with the lower oxygen flow rate from the results of XRD and four-point probe, respectively. On the other hand, with the higher growth temperature, the rougher surface morphologies, better crystal quality and higher electric conductivity of the films were obtained. From PL spectra, the intensity of green band (GB) emission was found to increase with the lower oxygen flow rate. In addition, the blue-shift NBE emission and depressed GB emission intensity resulted from the higher growth temperature can be interpreted as the enhanced electron carrier concentration and the reduction of oxygen-related defects, respectively.