以有機金屬化學蒸氣沉積法成長氮化鋁薄膜及其材料特性研究;Growth of Aluminum Nitride Epilayers by Metal- Organic Chemical Vapor Deposition

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Title:	以有機金屬化學蒸氣沉積法成長氮化鋁薄膜及其材料特性研究;Growth of Aluminum Nitride Epilayers by Metal- Organic Chemical Vapor Deposition
Authors:	林柏融;Lin,Bo-Rong
Contributors:	電機工程學系
Keywords:	氮化鋁;有機金屬化學蒸氣沉積法;深紫外發光二極體;AlN;MOCVD;UVC LED
Date:	2014-08-27
Issue Date:	2014-10-15 17:11:16 (UTC+8)
Publisher:	國立中央大學
Abstract:	近年來，以氮化鎵為基礎之藍綠發光二極體已廣泛應用於各種顯示器、背光源、室內照明等，而以氮化鋁鎵為基礎之深紫外光發光二極體也預期能應用於醫療光源、生物檢測或殺菌淨化用途，並期待能取代傳統汞燈。然而為了提升深紫外發光二極體之發光效率，在磊晶上有以下三點困難需要克服：(1) 氮化鋁(AlN)薄膜品質的提升，(2) P型氮化鋁鎵摻雜效率提升，(3) 量子井與能障之間的壓電極化造成波長紅移與效率下降。本研究利用有機金屬化學蒸氣沉積法成長AlN薄膜於藍寶石基板上，藉由調整中間插入層之厚度，於1180 ℃下成長1 m 厚之AlN薄膜，其AlN (102) X-光繞射搖幌曲線之半高寬為 583 arcsec，將高溫成長層厚度增加至3 m，其半高寬更下降至394 arcsec。在成長高鋁含量之N型與P型氮化鋁鎵於3 m 厚AlN薄膜之研究上也獲得一些成果，其中鋁含量60%之N型氮化鋁鎵成長到1 m 厚度時，其表面粗糙度僅0.63 nm，電子遷移率與載子濃度分別可以達到58 cm2/v-s與1.5×1019 cm-3，其特性已經與N型氮化鎵接近；而鋁含量30%之P型氮化鋁鎵之載子濃度僅達1.2×1016 cm-3，片電阻值高至1.04×105 ohm/sq，此部分仍然有待未來的突破。此研究亦成長氮化鋁鎵(AlGaN/AlGaN)量子井深紫外光發光二極體於氮化鋁薄膜上，並分析其發光特性。從陰極激發光譜可以發現，量子井發光波長為275 nm且半高寬為10 nm，與其他團隊相近，但仍需克服大部分電子容易與VAl-空缺復合，導致量子井發光微弱的問題。 ;In recent years, GaN-based light-emitting diodes (LEDs) have been widely applied in solid state lighting, displays, backlight and many other areas. AlGaN-based deep ultraviolet (UV) light-emitting diodes are also very promising as an alternative to traditional mercury lamps for applications in medical, bio-instruments and water purification systems. However, there are still several challenges to be overcome, including (1) insufficient AlN material quality, (2) low doping efficiency of p-AlGaN, and (3) large strain between the well and the barrier layers causing a strong piezoelectric field, which results in long emission wavelength and poor emission efficiency. This work was started with growing high quality aluminum nitride (AlN) epilayer on sapphire substrates by metal-organic chemical vapor deposition. By optimizing the thickness of the intermediate layer, 1 m-thick AlN epilayer grown at 1180 oC exhibited a full-width at half-maximum (FWHM) of the (102) x-ray diffraction rocking curve of 583 arcsec. For a 3 m-thick AlN, its FWHMs was decreased to 394 arcsec. The second part of this work was the growth of high Al-content n-type AlGaN. AlGaN epilayers with AlN mole fraction up to 0.6 were grown and characterization. A 1 m-thick n-type Al0.6Ga0.4N with roughness of 0.63 nm, mobility of 58 cm2/v-s and carrier concentration of 1.5×1019 cm-3 was achieved on a 3 m -thick AlN template. However, there is still much room to improve for p-type Al0.3Ga0.7N. Carrier concentration of 1.2×1016 cm-3 and sheet resistance of 1.04×105 ohm/sq was typically what was achieved on 1 m-thick p-type Al0.3Ga0.7N in this work. AlGaN deep ultraviolet light-emitting diodes on AlN buffer layer were fabricated and analyzed. Cathodoluminescence at 275 nm with FWHM of 10 nm was observed. However, the strong recombination between electrons and VAl- vacancies weakens the luminescence of quantum wells.
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