Abstract
There had various methods to generate the white light of SSL. Each method could be evaluated by cost, performance, and technology requirement. The research and challenge for industry or scientist was still in progress. The thesis was focus on the discussion of performance and technology requirement. The major technology now for III-nitride based LED fabricated including III-Nitride growth, doping, contact, etching and package was presented. How to make the high efficiency device was the research key point in this thesis. The solution was listed below in my research. ² Solution for Improvement of internal quantum efficiency We invented a photon-assisted wet etching with chopped photon source method for device fabrication. This damage free etching method could produce an ultra-smooth etching surface with RMS=0.37nm in GaN. The smooth, uniform, and broaden etching surface in GaN by ELPEC-CS was achieved. The methods was extended to etching p-type GaN, the physical limitation in photoelectrochemical etching was overcame. The first blue LED fabricated by photon-assisted wet etching method was fabricated. The surface treatment methods were also developed. The surface state was removed by boiled KOH treatment with short time or photon assisted cryogenic etching. The etching damage was the key issue while the device was scale down. ² Solution for Improvement of light extraction efficiency The light extraction method in the III-Nitride LED and III-Phosphide LED were developed by our photon-assisted wet etching method. ² Solution for Improvement of electrical efficiency n The p-type GaN issue was considered in hydrogen extraction and ohmic contact. The series resistance included resistance of p-type GaN and contact resistance were reduced and discussed in detail. n The scale-down effect of the III-Nitride structure and device was discussed. While the device scaling down, the current crowding effect will be suppressed. Many application of my research were presented including Digital light source and quick testing method. In the thesis, various structure sizes were fabricated by various etching technology. The size of III-Nitride based structure was fabricated from 300mm to 10nm. The LED structure from 300mm to 4mm could be formed by photolithography following by etching. By controlling photolithography in diffraction mode or over etching the metal mask, the size could be reduced from 2mm to 0.5mm. The mesa GaN LED or P/N diode could be fabricated. The nano structure from 100 to 30nm of GaN could be formed due to the dislocation-induced morphology during etching in photo-assisted wet etching. The structure with 50~10nm nano-wire could be fabricated in GaN or p-GaN during photo-assisted wet etching. The micro-LED was successfully fabricated. How to make the nano-LED with scale-down (100~0.1nm for nano scale) for III-Nitride was the major research in the future. The optimized device structure was designed by the commercial software with lattice mismatch control concept. The heat extraction in III-Nitride based flip chip LED and III-Phosphide vertical LED was designed. The scale-down effect of the thermal extracted was designed and discussion. There still had much challenges for fabricating or modeling while device was scale-down from micro to nano scale (100nm-0.1nm). The research and develop of micro-LED, nano-LED or quantum dot LED for “Next generation light source” was an interested, valuable and challenge work.