Quantum Optoelectronics

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.

Abstract:

Time-integrated and time-resolved microphotoluminescence studies have been performed on In x Ga 1 - x N quantum disks at the tips of GaN nanocolumns. The results are analyzed in the context of current theories regarding an inhomogeneous strain distribution in the disk which is theorized 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 disks under investigation. Internal field screening by an increased carrier density in the QDisks at higher excitation densities is observed via a blue-shift of the emission and a dynamically changing decay time. Other possible explanations for these effects are discussed and discounted. Cathodoluminescence studies have also been carried out on the nanocolumns to provide insight into the physical origin of the luminescence. © 2011 American Institute of Physics.

Abstract:

We have investigated exciton localization in binary GaN nanorods using micro- and time-resolved photoluminescence measurements. The temperature dependence of the photoluminescence has been measured, and several phonon replicas have been observed at the lower energy side of the exciton bound to basal stacking faults (I1). By analyzing the Huang-Rhys parameters as a function of temperature, deduced from the phonon replica intensities, we have found that the excitons are strongly localized in the lower energy tails. The lifetimes of the I1 and I2 transitions were measured to be < 100 ps due to enhanced surface recombination. PACS: 78.47.+p, 78.55.-m, 78.55.Cr, 78.66.-w, 78.66.Fd. © 2011 Park et al.