Showing papers by "Masao Nishioka published in 2008"

Coupling of quantum-dot light emission with a three-dimensional photonic-crystal nanocavity

Abstract: We report on the first demonstration of the coupling of fully confined electrons and photons using a combination of three-dimensional photonic crystal nanocavities and quantum dots. The three dimensional photonic crystals were assembled by stacking planar components using a sophisticated micromanipulation technique. Point defects, containing embedded quantum dots, were introduced into the photonic crystals as active sites. By measuring the photoluminescence spectra of the assembly, the process by which light emitted from the quantum dots is coupled to the defect modes of a three dimensional photonic crystal was demonstrated for the first time. The characteristics of the sharp emission peaks agreed well with numerical simulations, and these were confirmed to be resonant modes by polarization measurements. The highest quality factor (Q-factor) for three dimensional photonic crystals (2,300) was achieved.

Growth of high-uniformity InAs∕GaAs quantum dots with ultralow density below 107cm−2 and emission above 1.3μm

Abstract: We report the growth of high-uniformity large coherent InAs∕GaAs quantum dots (QDs) by metal organic chemical vapor deposition, with density between 106 and 1010cm−2, emission close to 1.4μm at room temperature with only GaAs capping, and temperature-independent peak linewidth as low as 14meV. It is shown that the QD density can be controlled by the InAs coverage, while the QD size remains remarkably constant. The observed decrease of the emission wavelength with coverage is explained by a density-dependent alloying. Microphotoluminescence measurement was performed on bare samples at 5K and single dot emission was observed.

Effects of accumulated strain on the surface and optical properties of stacked 1.3 μm InAs/GaAs quantum dot structures

Abstract: We report the effects of accumulated strain by stacking on the surface and optical properties of stacked 1.3 mu m InAs/GaAs quantum dot (QD) structures grown by MOCVD. It is found that the surface of the stacked QD structures becomes more and more undulated with stacking, due to the increased strain in the stacked QD structures with stacking. The photoluminescence intensity from the QD structures first increases as the stacking number increases from 1 to 3 and then dramatically decreases as it further increases, implying a significant increase in the density of crystal defects in the stacked QD structures due to the accumulated strain. Furthermore, we demonstrate that the strain can be reduced by simply introducing annealing steps just after growing the GaAs spacers during the deposition of the stacked QD structures, leading to significant improvement in the surface and optical properties of the structures. (C) 2007 Elsevier B.V. All rights reserved.