Electronic and photonic band engineering for novel optoelectronic and nanophotonic devices.

摘要

Fundamental electrical and optical properties of strained wurtzite InGaN/GaN-based quantum-well 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 quantum well. 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 efficiency, 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. (Abstract shortened by UMI.)