氧化鋅薄膜之光學及材料特性研究

Abstract

本研究中，我們比較三系列氧化鋅的樣品。在第一部分的研究中，我們研究三個結構相同但熱退火溫度不同的樣品，第二部分的研究我們研究生長在不同基板的氧化鋅，最後一部份我们研究不同厚度的p型及n型氧化鋅，樣品皆是以有機金屬氣相沉積的方式來成長的。在第一部分的研究中，我們以掃瞄式電子顯微鏡來觀察樣品表面的形貌，研究發現不同的熱退火溫度會造成樣品表面有不同尺寸的結晶顆粒，由X光繞射實驗我們觀察到樣品的結晶品質並不會隨著熱退火溫度提高而一直提升，在拉曼光譜的分析中，我們發現E1 (LO)的峰值強度及半高寬會隨著熱退火溫度提高而遞減。在光激發光譜中，我們可以觀察到二個發光的波段其中波長位於380nm的是由激子復合輻射所造成的，而另一個綠色發光是由晶格的缺陷的所產生，因此我們比較這系列樣品的綠光強度來決定樣品的最佳化生長條件。在第二系列的樣品中，我們以X光繞射實驗來判斷使用不同基板的樣品晶格常數，經由比較晶格常數，我們可以發現應力與發光峰值的關係。而從拉曼光譜，我們更可以確定應力和其光譜之間的關係，但是X光繞射實驗數據卻和無法與拉曼散射實驗結果符合，因此，在我們的研究中，無法發現到拉曼位移與應力的關係式。但是仍然可以觀察到拉曼散射的位移現象。在最後一系列的樣品實驗中，我們做了X光繞射、反射率、光激發光譜和拉曼散射實驗。由X光繞射可以得到樣品的品質，從反射率實驗們可以得到樣品薄膜的厚度，而光激發光譜可以得到樣品的缺陷強度，拉曼散射實驗可以了解樣品分子的對稱性，從這些實驗結果我們可以選擇出哪一片樣品有最好的品質，而從這片樣品的製程設定我們就可以很容易得得到高品質的氧化鋅薄膜樣品。

In this research, we compare three series samples of Zinc Oxide. For series one, we got three ZnO sample in the same epitaxy structure but with different annealing temperature. And the series two are the ZnO film which grown on different substrate. The last series are p-type and n-type ZnO thin film grown on Al2O3 with different thickness. All series were grown by metalorganic chemical vapor deposition (MOCVD). For series one (with different annealing temperature), the surface morphology was determined by scanning electron microscopy (SEM), it showed that difference of the grain size with different thermal annealing temperature. From XRD data we knew that the crystallinity quality of samples did not monotonously improve with annealing temperature. Using Raman scattering we could observe the annealed samples showed a decrease of the intensity and linewidth of E1 (LO) mode peak with increasing annealing temperature. From PL spectra, two emission bands were observed. One is the ultraviolet (UV) band with peak position at about 380 nm caused by the transition of excitons, and the other was the green band commonly referred to as a deep-level or trap-state emission caused by the defects of the crystal. So we compared the green band of this series samples to determine which one have the best quality that we know in what kind of the condition will get a high quality material. For series two (pair of ZnO grown on Si and sapphire), used the XRD we could find that the lattice constant of materials grown on different substrate. Comparing with the lattice constant and the UV peak shift, we could find the relationship between the stress and the PL peak positions. From Raman scattering spectra, we could find the more exactly relationship between stress and spectrum theoretically, but our XRD experiment results could not fitted the value of theory. Therefore, our research could not find the relation equation about Raman shift and stress. But the Raman shift was still observed. For last series, we were experimented with XRD, reflectance, PL and Raman scattering. The XRD would determine the sample quality and reflectance could find the thickness of film. PL showed the lighting efficiency and intensity of defect, and Raman spectrum represented the symmetry of material. Those experiment results were found the best quality of sample and to find the best fabricated condition of ZnO thin film materials.