Optical Studies Of Single Ingan Gan Quantum Dots

Author : Yingjuan Wang
Publisher :
ISBN 13 : 9781374667310
Total Pages : pages
Book Rating : 4.6/5 (673 download)

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Download or read book Comprehensive Optical Spectroscopic Investigations of Gan Epilayers and Ingan/Gan Quantum Structures written by Yingjuan Wang and published by . This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Comprehensive optical spectroscopic investigations of GaN epilayers and InGaN/GaN quantum structures" by Yingjuan, Wang, 王穎娟, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled COMPREHENSIVE OPTICAL SPECTROSCOPIC INVESTIGATIONS OF GaN EPILAYERS AND InGaN/GaN QUANTUM STRUCTURES Submitted by Wang Yingjuan for the Degree of Doctor of Philosophy at The University of Hong Kong in April 2006 Optical properties including non-linear optical properties and ultrafast phenomena, electronic structures, electron-phonon coupling and defect states of InGaN/GaN quantum structures and GaN epilayers were investigated by using a variety of optical spectroscopic techniques. Several theoretical models have been employed to simulate and interpret the experimental data. Strongly enhanced anisotropic lateral diffusion of photogenerated carriers in InGaN/GaN quantum wells (QWs) was directly observed using the luminescent imaging technique. In order to quantitatively interpret the phenomenon, enhanced ambipolar diffusion of carriers in such quantum structures due to the existence of a huge piezoelectric field was taken into consideration using the two-dimensional drift-diffusion equation. It is shown that the strong piezoelectric field and crystalline direction dependence of the carrier mobility are responsible for the enhancement and anisotropy of carriers'' lateral diffusion, respectively. Non-exponential decay behaviors of the photogenerated carriers in disordered InGaN/GaN QWs structures were experimentally observed and theoretically interpreted. The results show that electron and holes are not in the form of exciton but rather captured in different localized states independently when the amplitude of the disorder potential is higher than the binding energy of excitons. The carriers can either recombine or perform a phonon-assisted hopping transition between different localized states. The localization length of the photogenerated carriers, one of the most important parameters characterizing the disorder potential, was determined. The experimental temperature-dependent photoluminescence (PL) spectra of InGaN/GaN quantum wells and quantum dots were reproduced using the multimode Brownian oscillator (MBO) model with Ohmic dissipation. Excellent agreement between theory and experiment demonstrates not only the presence of strong electron-phonon coupling in InGaN/GaN quantum structures, but also that the dissipation due to the phonon bath modes of the surrounding matrices results in broadening of the PL spectral lines. These results show that the MBO model is suitable for quantitative interpretation of the PL spectra of InGaN/GaN quantum structures with the quantum dissipation giving rise to broadening of the PL line. Band gap renormalization and phase-space filling effects were observed in the InGaN/GaN QWs with Si-doped barriers. The experimental results show that Si doping in the barriers can lead to remarkable many-body effects in InGaN/GaN QWs light-emiiting diodes (LEDs). Optical nonlinear effects and weak temperature dependence of emission energies were observed and discussed in the dual emission-wavelength InGaN/GaN QWs LEDs. A detailed study on the damping of excitonic polaritons in GaN epilayers with varying background impurity concentrations was reported. The combined experimental and theoretical results show that the impurity scattering plays a dominant role in the damping of the propagating polaritons in GaN epilayers at low temperatures and significantly affects the lineshape of the low-temperature r