Showing papers by "Jean Massies published in 2013"
TL;DR: In this article, the authors reported an unusual temperature dependence of exciton lifetimes in arrays of GaN nanostructures grown on semipolar (11-22) oriented Al.
Abstract: We report an unusual temperature dependence of exciton lifetimes in arrays of GaN nanostructures grown on semipolar (11-22) oriented Al${}_{0.5}$Ga${}_{0.5}$N alloy by molecular beam epitaxy. Atomic force microscopy measurements revealed: (i) a one-dimensional ordering tendency along the [1-100] crystallographic direction together with (ii) an in-plane anisotropy of the nanostructure lateral shape with respect to [1-100] and [11-23] crystallographic axes. As a consequence, a morphological transition from dot-shaped islands forming an array of nanochains to wire-shaped objects elongated along the [1-100] direction was evidenced with the increase of the GaN deposited amount. Nanostructures of different dimensionality were fabricated including quantum dots (QDs), quantum wires (QWRs), and quantum wells (QWs), and the excitonic behavior was investigated as a function of the nanostructure shape. The measured temperature dependencies of the exciton radiative decay revealed its direct correlation with a spatial confinement, resulting in a temperature-independent exciton lifetime in the case of QDs, a square root dependence in the case of QWRs, and a linear dependence for QWs. These results, as well as absolute values of measured lifetimes, are in agreement with theoretical predictions.
55 citations
TL;DR: In this paper, the authors reported on the fabrication of ultraviolet (UV) light emitting diodes (LEDs) using GaN quantum dots (QDs) as emitters.
41 citations
TL;DR: In this paper, a light converter consisting of 10−40 InGaN/GaN quantum wells was used to grow a violet pump LED, which was adapted to avoid thermal degradation of the light converter.
Abstract: Monolithic InGaN-based light-emitting diodes (LEDs) using a light converter fully grown by metal organic vapor phase epitaxy are demonstrated. The light converter, consisting of 10–40 InGaN/GaN quantum wells, is grown first, followed by a violet pump LED. The structure and growth conditions of the pump LED are specifically adapted to avoid thermal degradation of the light converter. Electroluminescence analysis shows that part of the pump light is absorbed by the light converter and reemitted at longer wavelength. Depending on the emission wavelength of the light converter, different LED colors are achieved. In particular, for red-emitting light converters, a color temperature of 2100 K corresponding to a tint between warm white and candle light is demonstrated.
18 citations
TL;DR: In this paper, a reduction of the electroluminescence peak full width at half maximum (FWHM) is observed in self-assembled GaN quantum dots (QDs) grown on Al 0.5Ga0.5N.
Abstract: Self-assembled GaN quantum dots (QDs) grown on Al0.5Ga0.5N have been used as the active region of light emitting diodes (LEDs). The LED emission wavelength exhibits a strong shift towards higher energies with increasing current density, which allows obtaining an emission in the UV range (down to 375 nm) above 100 A/cm2. Together with this shift, a reduction of the electroluminescence (EL) peak full width at half maximum (FWHM) is observed. These features are a consequence of the quantum confined Stark effect caused by the built-in electric field in the heterostructure. At larger current densities, an opposite behavior (i.e., an increase of the FWHM) is observed concomitant with the appearance of an additional peak on the EL high energy side. This characteristic has been confronted with calculations and attributed to a transition between the lowest electron state and the first excited hole state in the QDs.
16 citations
TL;DR: In this paper, a numerical technique was developed to analyze quantitatively the dielectric properties and plasmon gas characteristics from infrared reflectivity measurements, based on the combination of Kramers-Kronig theorem with the classical theory of electromagnetic wave propagation in a system of thin films.
Abstract: We report on the application of infrared (IR) spectroscopy as an approach to nondestructive optical method for quantitative measurement of relevant optoelectronic properties in complex multilayer systems. We developed a numerical technique to analyze quantitatively the dielectric properties and plasmon gas characteristics from infrared reflectivity measurements. The developed technique is based on the combination of Kramers-Kronig theorem with the classical theory of electromagnetic wave propagation in a system of thin films. We applied the approach to deduce the dielectric properties and plasmon gas characteristics in p- and n-doped AlGaN alloys of various compositions, deposited on AlN(100 nm)/GaN(30 nm)/Al2O3. The results agreed with the electrical measurements, and the back calculation reproduced satisfactory the reflectivity measurements, demonstrating the accuracy of the developed technique.
13 citations