Student Number 942406012 Author Chi-wen Kuo(³¢©_¤å) Author's Email Address No Public. Statistics This thesis had been viewed 1222 times. Download 722 times. Department Optics and Photonics Year 2009 Semester 2 Degree Ph.D. Type of Document Doctoral Dissertation Language English Title The Optoelectronic Characteristics of Nitride-Based Light Emitting Diode Grown by Metal-organic Chemical Vapor Deposition Date of Defense 2010-06-04 Page Count 130 Keyword Blue LED Buffer layer GaN IPS LED Nano-rod GaN Abstract Through metal-organic chemical vapor deposition (MOCVD) to grow nitride-based materials, this dissertation mainly analyzes the characteristics of the nitride-based materials and optoelectronic semiconductor. The research focuses on GaN film and nitride-based blue LED, including advanced buffer layers, pendeo-expitaxy on nano-scaled template, and the development of nitride-based blue LED with the geometric sidewalls.
On one hand, we developed a double buffer layers- MgxNy/AlN. Judging from the result of X-ray analysis and Hall measurement, the high quality GaN could be obtained by the features of these buffer layers to reduce dislocation. Compared with GaN on conventional AlN buffer layer and MgxNy/AlN double buffer layers, the dislocation density of GaN film can be effectively reduced from 3.7¡Ñ108 cm-2 to 9.0¡Ñ107 cm-2 from the result of etching pits density (EPD).
On the other hand, we broke fresh ground in pendeo-expitaxy without lithographic process. We produced nano-rod GaN template (NR GaN template), with high aspect ratio by Ni as metal hard mask. By adjusting the growing condition, GaN was directly grown on NR GaN template without buffer layers. Judging from the result of Hall measurement and X-ray analysis, implementing pendeo-expitaxy to grow GaN film on the NR GaN template can acquire better quality. From result of EPD, the dislocation density of GaN film could be reduced to 1.9¡Ñ108 cm-2 by using NR GaN template. In addition, the following experiment makes further research on n-GaN/MQW/p-GaN LED structure directly grown on the NR GaN template. This has been profited by saving growth time of buffer layer and unintentionally doped GaN layer when LED structure was grown on nano-rod GaN template. In terms of the optoelectronic characteristics, there are no obvious differences in electronic properties between NR LED and C LED. The forward voltage is around 3.30V under the electronic current at a 20mA injection; in the meanwhile, the output power of NR LED promotes about 39.8% more than the C LED. The main factor in enhancing the light output power is focused on light extraction and internal quantum efficiency. Not only does the growth of pendeo-expitaxy form the void between the GaN/sapphire interface which increases the effects upon light scattering for light extration, but also the efficiency of internal quantum in NR LED up to 16.9% higher than in C LED which is only about 14.9%.
Last but not least, we enhance the light extraction efficiency of LED by making changes in geometric structure of LED chip die. We applied the feature of high chemical activity of GaN N-face and developed wet etching without lithographic process to change the sidewall of LED chip die. After the chip process, LED was deposited with SiO2 as hard mask, and then soaked in the mixed acid H2SO4 : H2PO4 = 3 : 2 at 250 oC for four minutes. After this wet etching process, the edge of LED chip die was etched as inverted pyramid structure. Finally, the residue of SiO2 was removed by utilizing buffered oxide etchant (BOE) to complete the fabrication of inverted pyramid sidewalls LED (IPS LED). Compared to conventional LED, it was found that the light output power of IPS LED has enhanced about 27% through the measurement of light characteristics. To go a step further, with the help of Prof. Wu in National Central University, it was found that inverted pyramid structure performs better on confined photons judging from the simulation of by finite-difference time-domain (FDTD). This statistics 24 % is similar to the practical result which reaches to 27%. Further, by taking advantage of the measurement of light power density, a light rectangle was discovered around the edge of IPS LED chip die. The intensity of the light rectangle is obviously higher than the conventional LED. This result responds to the stimulated statistics as well as interprets that inverted pyramid structure can indeed enhance light output power.
Table of Content ºKni
List of Tablesvii
List of Figures Captionsviii
Chapter 1 Introduction
Chapter 2 Introduction of Metal-organic Vapor Phase Epitaxy System
2.2Close-Coupled Showerhead Technology15
2.3In Situ Monitoring of Epitaxy Growth17
Chapter 3 Influence of MgxNy/AlN Double Buffer Layers in GaN Epilayer
3.3Characteristics of Unintentionally Doped GaN with Double MgxNy/AlN Buffer Layers37
Chapter 4 High Efficiency Nitride-based Blue LED Grown on Nano-rod GaN Template
4.2The Fabrication of Nano-rod GaN Template61
4.3Characteristics of Unintentionally Doped GaN epitaxial layer Grown on Nano-rod GaN Template62
4.4Characteristics of GaN-based Light-Emitting Diode Grown on Nano-rod GaN Template64
Chapter 5 High Light Extraction of Nitride-based Blue LED with Inverted Pyramid Sidewalls
5.2The Fabrication of GaN-based LED92
5.3The Experiment Procedure93
5.4Characteristics of Nitride-based Light-emitting Diodes with Inverted Pyramid Sidewalls95
Chapter 6 Conclusions and Future Works
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Advisor Cheng-huang Kuo(³¢¬F·×)
942406012.pdf Date of Submission 2010-07-20