金屬有機化學氣相沉積成長氮化銦鎵與氮化銦鋁合金在矽基板上用於光伏技術應用

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.