高效率奈米三族氮化物發光二極體之設計、磊晶成長分析與應用

Abstract

近年來三族氮化物被視為最具潛力製作高效率光電元件的材料之一，主因是其具有涵蓋從深紫外光到紅外光波段之直接能隙半導體材料特性，隨著磊晶成長和奈米級製程技術的開發與進步，不僅三族氮化物光電元件之效率提升，其應用範圍也愈加廣泛。然而，如何整合奈米級製程與磊晶成長技術以達到降低成長時的缺陷密度、增加光萃取效率、抑制量子侷限史塔克效應、改善電特性和提升載子復合及發光效率等等，一直是本領域當前最重要的研究課題。 本論文利用奈米製程開發、能帶結構設計和磊晶成長技術以改善上述問題。論文分為三部分，第一部分利用奈米壓印技術製作錐形二氧化矽圖形化基板以及內嵌式空氣孔洞模板，並分別成長氮化鎵發光二極體於其上，藉由降低缺陷密度和改善光萃取的方式提升發光二極體之效率；第二部分為高效率綠光發光二極體能帶結構設計，透過能帶工程模擬的方式，針對綠光發光二極體之多重量子井和電子阻擋層進行設計，以改善其因主動層銦含量較高所導致之效率不佳問題；第三部分為側壁式多重量子井奈米柱核殼結構綠光發光二極體之成長，於奈米柱頂部加上一層氮化矽鈍化層以抑制再成長時極化與半極化面的成長，增加非極性面主動層之成長面積並減輕量子侷限效應，同時達到控制磊晶面向、成長形貌和材料含量分佈的目的，進一步提升三維元件的可行性。 最後，本論文所提出之技術易於與當前成熟之光電元件製作方法進行整合，期望能提供未來新穎性光電元件在應用和製作上更多選擇。

Recently, III-nitride materials have been regarded as one of the most promising materials for developing highly efficient optoelectronic devices because their wide range of direct bandgaps covers the emission wavelength from deep ultraviolet (UV) to infrared (IR) region. With the development of epitaxial growth and nanoscale fabrication process, not only the performances of III-nitride-based optoelectronic devices have been enhanced, but also the applications of them have been extended. However, how to integrate nanoscale fabrication process with epitaxial growth technology to decrease the defect density of epitaxial layer, enhance light extraction efficiency, suppress quantum-confined Stark effect (QCSE), and improve the electrical properties, carrier recombination rate, as well as light emission efficiency of an optoelectronic device is the most significant issue facing this research area today. In this thesis, we use nanoscale fabrication process, band structure design, and epitaxial growth technology to solve the problems described above. The thesis consists of three parts: in the first part, we employed the technology of nanoimprint lithography (NIL) to fabricate cone-shaped silicon dioxide (SiO2) patterned substrate and embedded cubic air-voids template. The gallium nitride (GaN)-based light-emitting diodes (LEDs) were grown respectively on these two kinds of templates. Through the reduction of defect density and improvement of light extraction, the efficiency of LEDs can be greatly enhanced; in the second part, the band structures of green LEDs were investigated by using band diagram engineering and simulation. We focus on designing suitable structures for green LEDs, including multiple quantum wells (MQWs) and electron blocking layer (EBL), which can improve the inefficiency of conventional green LEDs caused by higher indium content in MQWs; in the third part, we proposed and demonstrated a new three-dimensional (3D) structure, purely sidewall InGaN/GaN core-shell nanorod green emitters. The core technology is introducing Si3N4 passivation layers on the topmost of nanorods to suppress the regrowth of polar and semipolar surfaces, leading to a large area of nonpolar active region. The large area of nonpolar active region can effectively release the QCSE of LED devices. With this methodology, we can control the growth surface, geometric shape, and material composition distribution of 3D devices simultaneously hence further enhancing their feasibility. Finally, the scheme proposed in this thesis is scalable and compatible with current technologies, which paves a new perspective for future application and development of optoelectronic devices.