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|Title: ||Electronic and Photonic Band Engineering for Novel Optoelectronic and Nanophotonic Devices|
|Authors: ||Xiao, Dong|
|Advisors: ||Dr. Ki Wook Kim, Committee Chair|
Dr. John M. Zavada, Committee Member
Dr. Gerald J. Iafrate, Committee Member
Dr. Salah M. Bedair, Committee Member
Dr. David E. Aspnes, Committee Member
|Keywords: ||photonic crystals|
left handed media
|Issue Date: ||17-Jul-2006|
|Discipline: ||Electrical Engineering|
|Abstract: ||Fundamental electrical and optical properties of strained wurtzite InGaN/GaN-based quantum-well (QW) structures are calculated based on the Rashba-Sheka-Pikus (RSP) Hamiltonian in the vicinity of the &Gamma point since the simple parabolic model is very poor to fit the valence band structures of the nitride wurtzite materials. The model includes the spontaneous and the strain-induced piezoelectric polarization, as well as the crystal-field and the spin-orbit interactions and the strain effect that are already included in the RSP Hamiltonian. The propagation method is used for the QW structure calculation and the nitride parameters were optimized based on the up-to-date experimental results and the theoretical calculations. It is found that the strain-induced piezoelectric field significantly alters the subband structure and determines the output intensity of the nitride quantum well light emitting diodes. The calculations are compared with the available experimental data of the nitride light emitting diodes (LEDs) and a good match exists for low In composition LEDs. For the case with high In composition (>0.2), the comparison between the calculations and the experiments supports the possibility of strain relaxation in the QW. The resulting model can accurately investigate the optoelectronic properties of nitride based QW LEDs over a wide range of In composition (<0.5). Based on the understanding of the polarization fields, a design that uses AlInGaN as the quantum barrier is proposed to control the strain, and thus the piezoelectric polarization field. So an efficient red emission can be realized, which is hard to achieve if GaN is used as the barrier. In the proposed design, three different InGaN/AlInGaN QW structures emit red, green and blue light with similar intensities. Also, to achieve high efficieny, important factors related to the oscillator strength are discussed in detail.
Since the initial predictions, photonic crystals (PCs) have offered new opportunities for realizing photonic integrated circuits with many important applications including optical communication and display. The feasibility of an electrically programmable PC is investigated theoretically based on the metal-insulator transition of vanadium dioxide (VO₂). We propose a slab structure based on VO₂ whose dielectric properties can be modulated by selectively applying the bias on a lithographically defined array of gate electrodes to induce the phase transition. So, unlike the ordinary PCs, wave propagation in the desired structure may be switched on/off or redirected as needed. To examine the idea, the optical properties of VO₂ in both the semiconducting and the metallic phase are investigated in the infra-red region. The photonic band structure and the wave guiding characteristics are studied by the iterative plane wave expansion (PWE) and the finite difference time domain (FDTD) methods. The results clearly indicate that the changes induced in the VO₂ dielectric properties via the phase transition can enable effective modulation of wave propagation at a high speed, offering a promising opportunity for a photonic circuit that can be programmed or reconfigured on demand.
The focusing effects in both ideal left-handed mediums (LHMs) and metallic photonic crystals (PCs) are investigated theoretically based on the finite difference time domain (FDTD) method. The analysis shows that the subwavelength resolution is possible in an ideal LHM system when the propagation loss is limited to 10⁻⁵ or smaller. However, image distortion may occur due to the interference effect. As for the metallic PC system, far-field images do appear at the opposite side to the source of the PC in the calculation. More importantly, the image location seems to follow the rule of geometric optics in respect to the changes in the source position as the direct proof of negative refraction in the PC-based system. The comparison between the ideal LHM and
the metallic PC suggests that the focusing effect in the PC-based system is different from that of the ideal LHM system in many aspects due to the inhomogeneous nature of the PC. Also the effect may not be solely determined by the photonic band structure and may require a negative effective dielectric constant. Finally, the calculation also indicates that the effective index of -1 can be realized in both the ideal metallic PCs and the realistic copper/silicon PCs.|
|Appears in Collections:||Dissertations|
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