Transmission Electron Microscopy Studies on InGaN/GaN Multiple Quantum Wells with H2 Process in Barrier Layers and ZnO Thin Films on GaN with Different Growth Temperatures
| Autor: | Chun-Yung Chi, 紀淳詠 |
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| Rok vydání: | 2005 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 93 In this research, we perform the optical and material analyzes of five InGaN/GaN multiple quantum wells of different H2 process conditions in growing barriers. Also, ZnO thin film structures on GaN grown at different temperatures are studied. The material analysis methods include high-resolution X-ray diffraction (HRXRD), high-resolution transmission electron microscopy (HRTEM), and strain state analysis (SSA) In optical characterization the fundamental optical properties are obtained with photoluminescence spectroscopy. We study the effect of H2 process in barriers of InGaN/GaN quantum well structures. In the PL results, we find that aggregation structures exist in the sample without H2 process. Also, the PL spectral peak vary over the wafer. In TEM results, we find that H2 process lead to stronger indium confinement in the well layers and can suppress the spinodal decomposition in the rim part of the wafer. By analyzing TEM images with SSA, we find that strong strains exist in the sample with H2 process such that spinodal decomposition become weaker. Besides, in 3D SSA images, we can see that the central part of the wafer have a better-defined quantum-well structure than that in the rim part. In XRD results, we find that the signal of quantum-well structures is quite strong in the central part of the wafer. Also, with the H2 process, the average content of indium in the sample is decreased. Then, we compare the nano-structures of three samples of ZnO thin films grown on GaN with different growth temperature conditions. Although disconnected spiral domain structures (at the order of 100 nm in width) were observed in the samples of high-temperature growth, the crystal quality is generally better than the one grown at the low temperature, either near the sapphire interface or far away from the interface. In the sample of high temperature growth through the whole process, the domain structures extend from the interface with a smaller scale and almost vertical sharp boundaries. The sample grown at the low temperature showed a connected structure from the interface. However, its crystal quality is quite poor. In the sample with initial low temperature growth and then high temperature growth, the ZnO layer started with a connected structure, like the sample of low temperature growth. However, it evolved into domain structures like the sample of high temperature growth beyond about 200 nm in thickness. The samples of high-temperature growth generally have higher photon emission efficiencies. The sample grown at the high temperature through the whole growth process has the highest quantum efficiency. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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