Study of Nanofabrication Techniques and Device Characteristics of High Efficiency GaN-based Light Emitting Diodes for Next-generation Solid State Lighting
| Autor: | Chiu, Ching-Hua, 邱清華 |
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| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 Recently, Nitride (III) light-emitting diodes (LEDs) with emission wavelength ranging from ultraviolet to the short-wavelength part of the visible spectrum have been intensely developed in the past 10 years. Due to the rapid developing in efficiency improvement, applying the opto-electronic device such as LED, laser and photo-detectors into our life becomes possible. Besides, because of the next generation application in optical storage, flat display, bio-detection and general lighting, the research about GaN lighting devices attracted more and more attentions. In this study, we mainly focus on developing GaN nano structures and applying these nano structures on GaN LED. The device fabrication process, efficiency improvement, material and opto-electronic characteristics of the nano-structured GaN-based LEDs will be also discussed. The entire dissertation could be divided into four parts. The first is developing a novel GaN nano structure fabrication process. By well control the metal depositing thickness, annealing temperature, etching conditions, we could achieve different length and diameter GaN nanorod arrays. The emission and anti0refelction characteristics of the fabricated nanorod structures will be discussed. Besides, we applied the valence force field model to help us to realize the influence of strain relaxation within GaN multiple quantum wells (MQWs). The second part of this dissertation is applying these nano structures on the surface of GaN-based LEDs to improve the lighting efficiency. We first utilizing etching method assisted by spinning nano spheres on device surface serving as masks to form high-aspect-ratio GaN nanorods. However, considered the possible deterioration of reduced current spreading paths, we then adopted a bottom-up method to synthesize ZnO nanorod on the surface to suppress the total internal reflection and improve the light extraction efficiency. The third method we used to improve the device performance is combing the overgrowth technique on nano-patterned sapphire substrate to improve the internal quantum efficiency (IQE) and light extraction efficiency simultaneously. At the later half of this dissertation, we focused on the studying of the IQE performance of GaN-based LEDs. We grow our LED structure on the patterned sapphire substrate (PSS) and an increment in IQE is expected. In the third part of this study, we modified the traditional method for IQE measurement. We firstly modify the excitation laser wavelength and a serious of power and temperature dependent study was performed to define the IQE of LED device. The internal carrier lighting mechanism was also studied. The last part of this dissertation is based on the third part but a electrical injection setup was established. This instrument enabled us doing a serious of temperature and injection current dependent measurement. It not only helped us understand more about the IQE, but also well for discovering the origins of efficiency droop phenomenon. Besides, simulation software of APSYS was also performed to simulate the device performance under different temperature. The output of this dissertation provided a great help on realizing the solid state lighting in next generation. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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