- 學位論文
以脈衝雷射蒸鍍法成長氧化鋅鎂合金的結構與光學特性研究
Growth and Optical Characterization of MgZnO Nanostructures by Pulsed Laser Deposition
摘要
本論文主要利用脈衝雷射蒸鍍法(pulsed laser deposition, PLD)，在c面sapphire(0001)基板上成長出純ZnO奈米柱。以及改變氧化鋅和氧化鎂的合金比例，成長MgxZn1-xO奈米結構。發現當靶材x增加時，會讓原本wurtzite結構的晶格常數c軸縮短，當x=0.5時只比純ZnO時的c軸減少0.85%，比起AlxGa1-xN(x=0.4)的2%小很多，表示MgxZn1-xO有較小的晶格變動，且從XRD分析上未看到有相分離的情況。從PL光譜分析，發現參雜氧化鎂可使紫外線peak藍移，可達3.47eV，這是由於MgO能隙高達7.6eV影響，因此可藉改變x值控制發光能隙。不過FWHM卻也跟著變寬，推斷是因為參雜鎂而使得晶格排列不整齊或者一些應力的不平均，造成能帶放光變寬。並且皆無藍綠光peak發生。再從Raman分析，由於皆無發現A1(LO)和E1(LO)，代表沒有因氧空缺或鋅原子空隙造成的空缺，為一品質優良的光學材料。而由過去文獻的PL能隙公式反推薄膜x值，發現和靶材x值並不一樣，對此做些討論。之後再針對成長環境，改變壓力、溫度、及發數，發現能隙皆會有所變化。
並列摘要
MgxZn1-xO is an important semiconductor alloy for applications in UV optoelectronics. In this thesis, we present a simple pulsed laser deposition method for the synthesis of MgZnO nanostructures. Nanostructured MgxZn1-xO thin films were grown on c-plane sapphire substrates at 700oC by pulsed laser ablation of a MgyZn1-yO (y ranging from 0.05 to 0.5) target under relatively high background oxygen pressure (5 – 10 Torr). The morphology of the sample was found to be strongly affected by the Mg content y of the target. Also, atomic force microscopy measurements showed that the surface becomes smoother as more Mg is incorporated. X-ray diffraction revealed that these nanostructured MgxZn1-xO films are epitaxial along the (0001) direction and the Mg content x increases with y, as expected. However, the achieved x (< 0.1) was much less than the Mg content (y) in the target. No phase separation was observed in all samples. The full width at half maximum of the x-ray diffraction peak increases with x, indicating the degradation of the crystalline quality, which is consistent with the results of Raman measurements. The room-temperature photoluminescence (PL) of the MgZnO nanostructured films is dominated by UV emission, which blueshifts with increasing x. The defect-related visible emission band was not observed in the PL spectra, which, together with the absence of A1(LO) and E1(LO) signals in the Raman spectra, indicates good optical properties of these samples. Moreover, the effects of growth parameters such as oxygen pressure, substrate temperature, growth time and growth rate, on the morphology and the optical properties of the deposited MgZnO nanostructured thin films were also studied in some details.