Quantum Optoelectronics

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.

Abstract:

Microphotoluminescence with one-photon and two-photon excitation has been employed to investigate localisation centres found in nanorod array LEDs. Quantum dot-like features with spectral width less than 1 meV were observed originating from low dimensional carrier confinement within the nanorods. Two-photon excitation was used to probe the individual localisation centres. The narrow peak PL energy does not shift with increasing excitation density, but rather an increase of discrete new peaks on the high energy side of the spectrum is observed. There is no temperature dependent emission energy shift observed from 4.3 K to 25 K. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

We report on the growth (using metal-organic vapour phase epitaxy) and optical characterisation of single and multiple layers of InGaN quantum dots (QDs), which were formed by annealing InGaN epilayers at the growth temperature in nitrogen. The size and density of the nanostructures have been found to be fairly similar for uncapped single and three layer QD samples if the GaN barriers between the dot layers are grown at the same temperature as the InGaN epilayer. The distribution of nanostructure heights of the final QD layer of three is wider and is centred around a larger size if the GaN barriers are grown at two temperatures (first a thin layer at the dot growth temperature, then a thicker layer at a higher temperature). Micro-photoluminescence studies at 4.2 K of capped samples have confirmed the QD nature of the capped nanostructures by the observation of sharp emission peaks with full width at half maximum limited by the resolution of the spectrometer. We have also observed much more QD emission per unit area in a sample with three QD layers, than in a sample with a single QD layer, as expected. © 2011 Elsevier B.V. All rights reserved.