Professor Robert Taylor

Abstract:

Semiconductor nanopyramids (NPs) provide advantages in the development of novel functional optoelectronic devices due to their unique size-dependent properties. Here we demonstrate a new method for the fabrication of selectively self-assembled single-crystalline GaN NPs on the m-plane of periodically strained GaN/InGaN multiquantum disks embedded in the middle of GaN nanorods. The GaN NPs, which have ~100 nm diameters and heights, are observed by scanning electron microscopy and their crystalline structure is confirmed by high-resolution transmission electron microscopy. Experimental analysis directly reveals the strain distribution along the growth direction of the NPs. Cathodoluminescence measurements on a single NP show that its emission energy redshifts compared with that of bulk GaN, corroborating the results showing the formation of tensile strain in the NP. Observations of the uniform distribution and localization of these NPs show the possibility of further tuning their size and density by controlling periodically strained nanorod surfaces.

Abstract:

In this paper, we report on the design, fabrication and characterization of a broadband photonic crystal filter. Modeling with a genetic algorithm (GA) was used to investigate the effect of changing the number of periods and thickness ratios of a photonic crystal filter structure with two alternating materials. Theoretical optimized parameters were obtained as a function of wavelength for a photonic crystal filter with a very broad filter bandwidth as well as a very narrow transmission window. We used the determined optimum parameters at a wavelength of 1550 nm to fabricate the structure using e-beam lithography and inductively coupled plasma (ICP) etching. Experimental results show that the structure indeed has a very narrow transmission window and a low loss of just 4 dB. Hence, this structure can be regarded as a high precision filter for optical communication and photonic integrated chip technologies. © 2012 Elsevier B.V. All rights reserved.

Abstract:

We propose an amplified all-optical polarization phase modulator assisted by a local surface plasmon in Au-hybrid CdSe quantum dots. When the local surface plasmon of a spherical Au quantum dot is in resonance with the exciton energy level of a CdSe quantum dot, a significant enhancement of the linear and nonlinear refractive index is found in both the real and imaginary terms via the interaction with the dipole field of the local surface plasmon. Given a gating pulse intensity, an elliptical polarization induced by the phase retardation is described in terms of elliptical and rotational angles. In the case that a larger excitation than the bleaching intensity is applied, the signal light can be amplified due to the presence of gain in the CdSe quantum dot. This enables a longer propagation of the signal light relative to the metal loss, resulting in more feasible polarization modulation. © 2012 Optical Society of America.

Abstract:

The optical properties of GaN nanocolumns containing pairs of In xGa 1-xN (x ∼ 0.1) quantum disks (QDisks) have been experimentally measured. Strain simulations reveal an inhomogeneous distribution of strain, and furthermore, a relaxation between successive QDisks along the growth direction of the column. Although this inhomogeneous distribution of strain may indicate a lateral separation of carriers in the QDisk, the decay lifetime of the emission suggests far less carrier separation. The quantum confined stark effect is found to create an inhomogeneous distribution of charge within the QDisks along the growth direction of the rod. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.