以同步輻射X光繞射實驗和量子蒙地卡羅方法來探討氧化鋅的應變及應力變化

Abstract

近年來氧化鋅材料已被廣泛的討論並且應用在半導體(發光二極體和表面聲波元件等光電元件)、醫學(牙齒修復和防曬相關產品)和傳統產業(橡膠製造工業與水泥工業等傳產)上。在本文中，我們利用脈衝雷射蒸鍍系統在不同的基板上成長高品質的氧化鋅磊晶薄膜，其中使用的基板包括藍寶石基板與使用奈米厚度的氧化鋁(Al2O3)或氧化釔(Y2O3)材料當作緩衝層的矽基板。

在本論文當中，我們主要著重在探討氧化鋅的彈性模量與其相關的物理性質，其中主要分成實驗和模擬計算兩部份來做研究:(1)利用同步輻射X光繞射來量測氧化鋅的應變變化及其內部所受的應力數據。(2)模擬計算在密度泛函理論的架構下，保留LDA與GGA，之後並進一步超越密度泛函理論使用了混合函數近似的方式，如PBE0和B3LYP等混合函數計算方法，藉由其來改善計算應變趨勢的誤差，(3)此外我們也使用量子蒙地卡羅法來計算材料的應變變化、體積模量與帕松比。

根據研究結果顯示:(1)密度泛函理論計算無法完整描述氧化鋅的應變趨勢，其應變的定性趨勢並不正確(在拉伸的部份是跟實驗值相反)，(2)量子蒙地卡羅法的計算則使應變趨勢與實驗數據一致並使體積模量的計算更加精確。

In recent years, the Zinc Oxide material has drawn broad attentions and has been widely used in the semiconductors (like the Light-Emitting Diodes, the Surface Acoustic Wave devices and the other optoelectronic devices), medical (dental restoration and sun protection products) and conventional industries (rubber manufacturing industry and the cement industry and etc. ).We use a pulsed laser deposition system to grow high-quality epitaxial zinc-oxide thin film on different substrates, e.g. sapphire or silicon, where the later requires buffer layers like Al2O3 or Y2O3.

In this thesis, we mainly focus on studying the modulus of elasticity and the physical properties of Zinc Oxide. There are two main parts in this study: (1) XRD experiments, using the synchrotron radiation (hard x-ray diffraction) to measure the uniaxial strains of Zinc Oxide and calculate the internal stress. (2) density-functional calculations with exchange correlation functionals treated by LDA, GGA, and hybrid functionals, where hybrid functionals used here include PBE0, and B3LYP. These hybrid functionals improve the calculated strains. (3) In addition, we also use the Quantum Monte Carlo method to calculate the strains, the bulk modulus and the Poisson’s ratio.

According to the final results: (1)the density-functional calculations do not give qualitatively correct strains (the calculated tensile is the opposite of the experimental measurement). (2) Quantum Monte Carlo obtains the strains, including the bulk modulus, consistent with the experimental data.