Metal Organic Chemical Vapor Deposition Growth of
Tran, Binh Tinh
Chang, Edward Yi
|Abstract:||本論文的主要目標是發展寬能隙InxGa1-xN 與InxAl1-xN 於矽基板上以應用於太陽電池，研究中使用高含量In 以提升光伏元件的效能。三五族-氮化物半導體材料包含氮化銦，氮化鋁，氮化鎵與它們的合金等材料，由於其為直接帶隙材料並具備從紅外光到紫外光的寬廣光譜範圍，因此將其應用在光伏元件方面將有極高潛能。但是，由於InN 和GaN 之間晶格常數差異極大，意味這兩種材料之間的低溶解度進而導致固相混溶間隙，因此欲成長高結晶品質的InxGa1-xN 於矽基板上將具有高難度的挑戰。在本研究中，使用金屬有機化學汽相沉積（MOCVD）並設計緩衝層結構以達到控制缺陷和相位分離的目的。In 含量約40%的異質結構InxGa1-xN/GaN 已被成功長在Si(111)基底上並製作成高轉換效率的太陽能電池。
n-In0.4Ga0.6N/p-Si 異質接面太陽能電池被製作於矽基板上，上下電極則分別使用ITO (或Ti/Al/Ni/Au) 與Al 等材料。在本研究中也進行了比較ITO 為n 型接觸和使用Ti/Al/Ni/Au 為n 型接觸的太陽能電池原件。使用ITO 為N-電極之太陽能電池元件顯示出之開路電壓(VOC)為1.52 V、短路電流密度(JSC)為8.68 mA/cm2、填充因子為54%，太陽能電池之光電轉換效率與外部量子率 (EQE) 分別為7.12 和20.8%。其中，InGaN材料中In 含量與Voc 關係也被深入討論。本研究中亦使用有機金屬氣相化學沉積系統(MOCVD)成長不同In 成分(x = 10.2, 16.2 and 17.6%)之InxAl1-xN/GaN 於矽基板上。In0.176Al0.838N/GaN 結構之紫外線光電二極體元件顯示出極低leakage current (0.12 μA)，高光譜響應和良好的量子效率(94 mA/W 和44% 在 265 nm)。|
The main objective of the dissertation is to develop wide bandgap InxGa1-xN and InxAl1-xN on Si substrates for photovoltaic applications (solar cell and ultraviolet photodiode) with high In content that can be integral component of photovoltaic devices to achieve high efficiency. The III-Nitride semiconductor materials, which consist of InN, AlN, GaN, and their alloys, have a high potential in the development of high efficiency photovoltaic due to its wide direct bandgap cover a spectral range from the infrared to the ultraviolet, electronic and optical properties. However, the growth of high-crystalline-quality InxGa1-xN films in the full composition range is also highly challenging because the large lattice mismatch between InN and GaN causes a solid-phase miscibility gap due to the low solubility between these two materials. This is one of the major challenges for the growth of InxGa1-xN and InxAl1-xN on any substrates. In this present work, by improving the buffer layer, controlling defects and phase separation using Metal Organic Chemical Vapor Deposition (MOCVD). The heterostructure InxGa1-xN/GaN with about 40% In content and lattice-matched InxAl1-xN to GaN were successfully grown on a Si (111) substrates and fabricated into solar cell and ultraviolet photodiode devices with very high conversion efficiency. The research includes three approaches. The electro-optic characteristics of a n-In0.4Ga0.6N/p-Si hetero-structure solar cell on Si substrate with Al and ITO (or Ti/Al/Ni/Au) materials for p and n-type contacts were grown, fabricated and investigated. The solar cell devices with ITO as n-type contacts were also compared to the solar cell using Ti/Al/Ni/Au as n-type contact in this study. The device with ITO contact exhibited an open-circuit voltage (Voc) of 1.52 V and a short-circuit current density (Jsc) of 8.68 mA/cm2 with 54% fill factor. The conversion and external quantum efficiency (EQE) of the solar cell were 7.12 and 20.8%, respectively. Besides, a relationship between VOC and In content in the InxGa1-xN alloys for this type of solar cell was also derived. High quality InxAl1-xN/GaN hetero-structures were also grown on Si substrates with various indium compositions (x = 10.2, 16.2 and 17.6%). The ultraviolet photodiode fabricated based on In0.176Al0.838N/GaN structure shows excellent device characteristics with a low leakage current of 0.12 μA, and a high spectral response. It has good quantum efficiency of 94 mA/W and 44% at 265 nm.
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