在本論文中，我們探討氮化鉻緩衝層對氮化鎵薄膜的影響，相較於未使用緩衝層的情況，20 nm厚度的氮化鉻緩衝層能改善後續氮化鎵的結晶品質及光學性質。由SEM表面形貌圖得知無氮化鉻緩衝層的氮化鎵薄膜表面有“ㄑ”狀突起，且每個突出端都有缺陷存在；氮化鉻緩衝層20nm厚度的的氮化鎵薄膜表面平整許多；氮化鉻緩衝層40nm厚度的氮化鎵薄膜表面非常不平整且缺現超多。由ω-2Θ及ω掃描兩軸(a軸及c軸)方向的量測結果，有氮化鉻緩衝層20nm厚度的氮化鎵薄膜半高寬均最小，分別為322arcsec,1840 arcsec及1450arcsec，因此證實20 nm厚度的氮化鉻緩衝層能改善後續氮化鎵的結晶品質。再由光致螢光(PL)低溫及變溫量測結果，得知無氮化鉻緩衝層的氮化鎵薄膜除了近能帶發光外，缺陷發光明顯；氮化鉻緩衝層20nm厚度的的氮化鎵薄膜近能帶發光峰強度大半高寬小且缺陷發光峰很微弱；氮化鉻緩衝層40nm厚度的氮化鎵薄膜近能帶發光微弱，反之，缺陷發光峰相對強度大。由此證實20 nm厚度的氮化鉻緩衝層能改善後續氮化鎵的光學性質。

The results of the SEM image indicate that the surface morphology could be controlled by using different buffer layer. For the GaN film with LT-GaN buffer layers buffer layer, the SEM image with striated morphology overlaid with faceted ‘‘arrow’’ pattern and many pits placed at the corners. Relatively, the SEM images of the GaN films with LT-GaN and CrN buffer layer 20nm did not show the striated morphology and more smooth. However, The surface morphology of the GaN film with LT-GaN and CrN buffer layer 40nm is very rough and includes a lot of dislocations.
The crystalline characteristics of GaN film with various buffer layer by the HRXRD rocking curves (XRCs) are investigated. The crystal quality of the GaN film with LT-GaN and CrN buffer layer 20nm is the best, since the full width at half maximum (FWHM) in a-axis is the narrowest (1840arcsec). Furthermore, the full width at half maximum (FWHM) in c-axis is also the narrowest(1450 arcsec) of the three samples.
While we compared to the optical characteristics of the GaN film with various buffer layer , the GaN films with LT-GaN and CrN buffer layer 20nm show the common GaN near bandedge emission (3.47eV) and the defect peaks of GaN film are not obviously. The result, we demonstrate that the crystalline and optical property of GaN thin film has been improved by inserting optimum CrN buffer layer thickness.

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