氮化銦奈米點之微拉曼光譜和應變分析

Abstract

本篇論文主要是利用微拉曼光譜(□-Raman)實驗技術去研究有關氮化銦奈米點(InN nano-dots)不同形貌下對應變(strain)造成的影響。 隨著不同量子點的形貌，我們觀察到拉曼散射(Raman scattering)的E2模態有明顯的位移，經交叉比對數據後發現當量子點的高寬比越小則氮化銦奈米點的拉曼E2模態頻率有明顯增加的情形。再藉由X光繞射實驗得到樣品的應變(strain)大小與拉曼E2模態頻率的對應關係。利用拉曼散射E2模態的頻率，以及對應的X光繞射結果，搭配文獻上的理論計算結果，再擬合實驗結果後。我們可以求出在零應變(strain-free)下，氮化銦E2模態的頻率，也可反推出奈米點剛形成時所受殘餘的應變(residual strain)大小。 由於氮化銦奈米點與緩衝層(buffer layer)的熱膨脹係數(thermal expansion coefficient)不一樣，所以從高溫冷卻到室溫的過程中會有殘餘的熱應變(residual thermal strain)，我們對不同的長晶溫度的氮化銦其殘餘的熱應變也作分析，結果得到：氮化銦在形貌上所造成的應力遠大於溫度所造成的熱應變，甚至成長方式的不同也對氮化銦形成時所產生的應變(strain)影響甚小，因此我們對此兩種情形所可能造成的應變皆予以忽略不計。

In this thesis,we studied the realationsheep between the strain and the different size InN nano-dots by □-Raman and X-ray diffraction(XRD). The Obvious shift of Raman E2 mode is observed with different size InN nano-dots. As the aspect ratio decreased, we found the compressive strain increased. The strain variation versus aspect ratio could be fitted well by 2D thick ribbon model and it was used for elastic relaxation process of island growth.We could determine the initial strain around 0.42 % with the Raman scattering and X-ray diffraction after primary plastic relaxation and also obtained the slope coefficient between Raman E2 mode and residual strain.The thermal expansion coefficients of InN nano-dots and buffer layer are different from each other, so the residual thermal strain results from that high temperature cool down to room temperature.We found that residual thermal strain can be neglect because of the small by calculation.