以拉曼量測分析氮化鎵材料品質之方法

Abstract

在圖案化藍寶石基板(Patterned Sapphire Substrates, PSSs)上利用MOVCD 成長氮化鎵薄膜可以有效減少穿隧差排密度(Threading Dislocation Density)及讓磊晶品質變好，以達到降低缺陷密度(defect density)的用意。以往都是利用X 光繞射分析儀(X-Ray Diffractometer , XRD)來量測晶格常數(Lattice constant)並探討其應力跟應變之關係，以及使用Etching pit density(EPD)來觀測差排密度(dislocation density)，拉曼量測會因為聲子振動模式的不同而能量到不同模態的拉曼位移(Raman shift)，由此便可得知其應力變化，所以我們假設能以拉曼量測來取代XRD 以及EPD 所能做到的功能，並用實驗來進行驗證，這是以往沒有嘗試過的領域。在此實驗使用單一週期業界量產型圖案化藍寶石基板，以同樣參數成長不同厚度之氮化鎵，我們發現隨著改厚度不同，而受到不同的應力，且此應力會影響到後續製成電子元件之使用效率。最後論文會探討比較 XRD 與EPD 及拉曼之間應力與缺陷密度並以穿透式電子顯微鏡(Transmission Electron Microscope ,TEM)來驗證，發現拉曼會比XRD 來的更精準，且能與EPD 之結果有所相符，表示以後使用拉曼即可做到上述實驗中所能做到的事情，進而提高電子元件之使用效率及降低成本。

Using Metal-Organic Chemical Vapor Deposition to grow gallium nitride thin film on a patterned sapphire substrate can reduce the threading dislocation density and increase the crystal quality, and reduce the defect density (defect density).Most of literature were metioned that using XRD to measure lattice constant to compare the relationship between stress and strain,and using EPD to get dislocation density.Because of the difference of vibration mode of phonon,we can measure different Raman shift. We can analyze the difference of stress from Raman shift.Therefore we supposed that we can use μ-Raman to replace XRD and EPD.So we do experiment to prove it.We use same recipe to grow GaN with different thickness on commercial patterned sapphire substrate which have single period microstructure; however , we have different thickness GaN on the sapphire substrate, but we found that with the change of the thickness of the GaN, gallium nitride crystal growth will present two very different faces,and are subject to different stress, which can affect the efficiency of the use made of the subsequent electronic components.In the final stage, this paper will discuss the stress and defect density with different methods and use Transmission electron microscope to observe the phenomenon of dislocation . We find out that the measurement by Raman is more accurate than XRD.Using Raman will be a trand in the future . Thus improving efficiency of electronic devices which was grown on the gallium nitride thin film.