氧化鋅及摻鎵氧化鋅之奈米結構與光學特性

The Nanostructures and Optical Properties of ZnO and ZnO:Ga

黃俊傑(jyun-jie huang)

指導教授 ： 洪魏寬

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2007年)

摘要

本研究分為兩部份，第一部份為未摻雜氧化鋅奈米線之成長。首先我們利用熱蒸鍍法的方式成長出垂直於a-plane sapphire基板上的氧化鋅奈米線，並改變氧化鋅蒸發源質量的方式去控制氧化鋅奈米線之線徑，分別成長出線徑約為20nm、40nm、60nm、100nm的奈米線。而這些奈米線的成長方向均垂直於基板，由TEM電子繞射圖得知成長方向為[0001]。另外在PL量測發現奈米線線徑愈小，UV發光帶會有藍移現象，由變溫及變激發功率PL實驗推論為表面激子所致。另外我們也調整製程參數來控制氧化鋅奈米線之長度，發現奈米線長度愈長其PL放光強度愈強，由PL及Raman量測中推論出較短之奈米線受到基板不匹配的問題造成張應力(tensile stress)的發生而使得奈米線底端部分累積較多缺陷，因此在放光時非輻射放射機率提高造成發光強度之衰減。
第二部份為摻雜鎵之氧化鋅奈米線與奈米帶之成長與分析，首先在摻雜鎵奈米線方面，SEM顯示摻雜比例提高奈米線方向性也愈差，且變的比較稀疏。由TEM量測得知摻雜後的奈米線成長方向均為[0001]，而在摻雜過量下其結晶品質變差。在PL量測中發現適當比例的摻雜可以提高其放光強度。最後在摻雜鎵奈米帶的部份，從PL光譜中得知摻雜鎵後其放光強度的提升，而強度的增加與鎵的摻雜形成雜質相關放射有關。此外並發現在摻雜10%之蒸發源的奈米帶其UV發光帶有明顯藍移。在低溫PL中我們發現隨著摻雜比例的增加其中一個束縛激子的峰值位置有明顯之位移，因此我們推論出由於摻雜鎵使得束縛激子易於產生，並與室溫PL UV發光帶之位移相關。 此外從Raman的量測得知在適當摻雜鎵後可以提高結晶品質，而這也是影響PL放光強度的主因之一。

關鍵字

熱蒸度法 ； 氧化鋅 ； 氧化鎵 ； 奈米線 ； 摻雜

並列摘要

This thesis consists of two parts .In the first part, well-aligned vertical ZnO nanowires were grown on the a-plane sapphire substrates by thermal evaporation. X-ray diffraction and transmission electron microscopy analyses confirmed that the nanowires are c-axis orientated. We found that the diameter of the nanowires can be controlled by the amount of the source materials. The diameters of grown nanowires ranged from 20nm to 100nm.The UV emission of the photoluminescence(PL) blueshifts with decreasing wire diameter. This blueshift may be attributed to the increased surface to volume ratio and the existence of a surface-related emission. Power-dependent and temperature-dependent PL measurements supported this suggestion.
Furthermore, the length of ZnO nanowires with approximately the same radius can be controlled by varying the growth time.PL measurements showed that longer wires have stronger UV emission. Raman measurements show the ZnO E2(high) mode red-shifts with decreased wire length. We infer that the defects becomes less as the nanowires get longer, finally leading to higher PL intensity.
In the second part, we had grown Ga-doping of ZnO nanowires and nanobelts on a-plane sapphire substrates. The selected area diffraction pattern showed that the nanowires growth direction was [0001]. The increase in PL intensity due to Ga doping was attributed to the increase of Ga donor-related impurity emission. However, excess Ga atoms could create nonradiative recombination centers, such as impurity-assisted nonradiative transition channels, resulting in a reduction of the near band edge luminescence. Raman spectrum showed that the ZnO E2(high) mode intensity enhances when the nanobelts were doped with suitable Ga, which implies the improvement of crystal quality.

並列關鍵字

thermal evaporation ； zinc oxide ； gallium oxide ； nanostructures ； doped

參考文獻

[1] Daihua Zhang, Chao Li, Xiaolei Liu, Song Han, Tao Tang, and Chongwu Zhou,

Appl. Phys. Lett. 83, 9 (2003)

[5] Hsu-Cheng Hsu, Chun-Yi Wu, and Wen-Feng Hsieh, Appl. Phys. 97, 064315 (2005)

[6] B. Meyer and Dominik Marx, Phys.Rev.B67, 035403 (2003)

[8] P.Yang and C.M. Lieber, Science 273, 1836 (1996)