Quantum Optoelectronics

Abstract:

Cavities embedded in photonic crystal waveguides offer a promising route towards large scale integration of coupled resonators for quantum electrodynamics applications. Here a strongly coupled system consisting of a single quantum dot and a cavity formed by the local width modulation of a photonic crystal waveguide is demonstrated. The resonance originating from the cavity is clearly identified from microphotoluminescence mapping of the scattered signal along the waveguide. The exciton-photon strong coupling regime is obtained by temperature control. © 2011 American Institute of Physics.

Abstract:

Microphotoluminescence studies were carried out on a single GaN nanocolumn containing a single InGaN quantum disk (QDisk) that had been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system. © 2011 American Institute of Physics.

Abstract:

Time integrated and time resolved microphotoluminescence studies have been performed on InxGa1-xN quantum disks embedded in GaN nanocolumns. The results are analysed in context of current theories regarding an inhomogeneous strain distribution in the disk, which is theorised to generate lateral charge separation in the disks by strain induced band bending, an inhomogeneous polarization field distribution, and Fermi surface pinning. It is concluded that no lateral separation of carriers occurs in the quantum discs under investigation. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Abstract:

Ultrafast non-equilibrium carrier dynamics and many body effects have been investigated in GaN beyond the Mott density. The transient (∼1 ps) induced absorption was observed near the band edge due to band gap renormalisation; collision broadening and temporal evolution of the mean carrier energy were also obtained experimentally. The development of the longitudinal optical (LO)-phonon induced non-thermal electron distribution observed in the pump-probe at early times (≤1 ps) was in excellent agreement with a Monte-Carlo simulation, where the mean carrier energy loss rate of screened carrier-phonon interactions was found to be further reduced due to the hot phonon effect. Schematic diagram of non-equilibrium carrier dynamics. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

Microstructural characterisation of a heterostructure containing an In xGa1-xN/InyGa1-yN super-lattice sacrificial layer (SSL), an AlGaN etch stop layer and an InGaN quantum dot layer has been carried out. These structures are intended for photo-electrochemical etch mediated fabrication of undercut microdisks and were found to generate additional dislocations due to the additional strain energy imposed by the growth and inclusion of the InGaN quantum dot layer. Micro-photoluminescence was also carried out and showed the unexpected formation of quantum dots within the SSL. An equilibrium critical stack thickness model corresponding to the total thickness of the heterostructure that would favour the additional generation of dislocations was formulated through an energy-balance consideration. This correlated well with the experimental results and a prediction of the SSL indium composition for the full structure that would not lead to additional dislocation generation could thus be made. © 2011 Elsevier B.V. All rights reserved.