Showing papers by "Le Si Dang published in 2013"

AlGaN/AlN quantum dots for UV light emitters

Abstract: We report on the growth and properties of two types of AlGaN/AlN nanostructures: Stranski-Krastanow quantum dots (SK-QDs) and nanodisks (NDs) created by nanowire heterostructuring. In both cases, the emission wavelength can be tuned in the range of 240-350 nm at room temperature by varying the flux ratio and the nominal amount of AlGaN in the nanostructures. The efficient carrier confinement in these nanostructures leads to an internal quantum efficiency around 0.5. However, the emission spectra of AlGaN/AlN NDs show broader linewidth than those of SK-QDs, which is attributed to inhomogeneities in height and in chemical composition. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Strong Carrier Localization and Diminished Quantum-confined Stark Effect in Ultra-thin High-Indium-content InGaN Quantum Wells with Violet Light Emission

Abstract: Here, we report on the optical and structural characteristics of violet-light-emitting, ultra-thin, high-Indium-content (UTHI) InGaN/GaN multiple quantum wells (MQWs), and of conventional low-In-content MQWs, which both emit at similar emission energies though having different well thicknesses and In compositions. The spatial inhomogeneity of In content, and the potential fluctuation in high-efficiency UTHI MQWs were compared to those in the conventional low-In-content MQWs. We conclude that the UTHI InGaN MQWs are a promising structure for achieving better quantum efficiency in the visible and near-ultraviolet spectral range, owing to their strong carrier localization and reduced quantum-confined Stark effect.

Toward Room Temperature One-Dimensional Quantum Fluid in the Solid State: Exciton Polaritons in Zinc Oxide Microwires

Abstract: Exciton-polaritons in semiconductor nanostructures constitute a model system of quantum fluid of ultra light Bose excitations in a driven-dissipative situation. Owing to recent progresses in the domain of nanofabrications, polaritons environment may now be tuned at will in terms of external potential and dimensionality. In this chapter we present a nanostructure of particular interest to generate and manipulate one dimensional polaritons with unusual properties: ZnO microwires. Within such a structure we show that polaritons are stable at room temperature and have the property of being strongly decoupled from the lattice thermal vibrations, therefore naturally protected from thermal decoherence. We also find that at cryogenic temperature, the 1D superfluid phase is surprising as polaritons are much heavier than usual and quasi purely excitonic in nature. At room temperature, another polariton superfluid phase is also observed, and several experimental facts indicate that the strong coupling is well preserved in spite of a much larger critical density.