Design, Epitaxial Growth, Characterization and Applications of Nanoscale III-Nitride Light-Emitting Devices with High Performance
|關鍵字:||發光二極體;三族氮化物;磊晶;奈米結構;Light-emitting diode;III-nitride material;Epitaxy;Nano-structure|
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.
|Appears in Collections:||Thesis|