Composition and luminescence of AlInGaN layers grown by plasma-assisted molecular beam epitaxy

A study of AlInGaN epilayers, grown by plasma-assisted molecular beam epitaxy, was performed using spatially resolved x-ray microanalysis and luminescence spectroscopy in order to investigate competition between the incorporation of In, Al, and Ga as a function of the growth temperature in the 565-660 °C range and the nominal AlN mole fraction. The samples studied have AlN and InN mole fractions in the ranges of 4%-30% and 0%-16%, respectively. Composition measurements show the effect of decreasing temperature to be an increase in the incorporation of InN, accompanied by a small but discernible decrease in the ratio of GaN to AlN mole fractions. The incorporation of In is also shown to be significantly increased by decreasing the Al mole fraction. Optical emission peaks, observed by cathodoluminescence mapping and by photoluminescence, provide further information on the epilayer compositions as a function of substrate temperature, and the dependencies of peak energy and linewidth are plotted

Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities

Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial (Al,Ga)N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The λ/2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5 K: anticrossing with a normal mode splitting of 43±2 meV and 56±2 meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance

(In,Ga)N/GaN microcavities with double dielectric mirrors fabricated by selective removal of an (Al,In)N sacrificial layer

Comparable microcavities with 3/2 (~240 nm) active regions containing distributed (In,Ga)N quantum wells, grown on GaN substrates and bounded by two dielectric mirrors, have been fabricated by two different routes: one using laser lift-off to process structures grown on GaN-on-sapphire templates and the second using freestanding GaN substrates, which are initially processed by mechanical thinning. Both exploit the properties of an Al0.83In0.17N layer, lattice matched to the GaN substrate and spacer layers. In both cases cavity quality factors >400 are demonstrated by measurements of the cavity-filtered room-temperature excitonic emission near 410 nm

TEM Nanostructural Investigation of Ag-Conductive Filaments in Polycrystalline ZnO-Based Resistive Switching Devices

Memristive devices based on a resistive switching mechanism are considered very promising for nonvolatile memory and unconventional computing applications, even though many details of the switching mechanisms are not yet fully understood. Here, we report a nanostructural study by means of high-resolution transmission electron microscopy and spectroscopy techniques of a Ag/ZnO/Pt memristive device. To ease the localization of the filament position for its characterization, we propose to use the guiding effect of regular perturbation arrays obtained by FIB technology to assist the filament formation. HRTEM and EDX were used to identify the composition and crystalline structure of the so-obtained conductive filaments and surrounding regions. It was determined that the conducting paths are composed mainly of monocrystalline Ag, which remains polycrystalline in some circumstances, including the zone where the switching occurs and at secondary filaments created at the grain boundaries of the polycrystalline ZnO matrix. We also observed that the ZnO matrix shows a degraded quality in the switching zone, while it remains unaltered in the rest of the memristive device

Growth and fabrication of gaN-based structures using aluminium indium nitride insertion layers

This speech was presented to the 2005 Annual Conference of the British Association for Crystal Growth, held in Sheffield on Sunday 4 - Tuesday 6 September 2005. The presentation focused on the design and growth of microcavities and the roles of AlInN layer in post-growth processing

Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods

Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N / AlN Bragg mirror followed by a lambda/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2,mu m thick GaN layer is grown, and progressively thinned to a final thickness of lambda. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity spectra of the microcavities are well accounted for by using transfer matrix calculations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3477450

Correlating Composition and Luminescence Variations in AlInGaN epilayers

Epilayers of the quaternary alloy AlxInyGa1 x yN have been grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy. The emission properties and elemental compositions of these samples were evaluated simultaneously and intercorrelated by combining hyperspectral cathodoluminescence imaging and wavelength-dispersive X-ray mapping. Use was made of inherent variations in growth temperature across a single epilayer to study the resultant effect on the different metal fractions and luminescence emission wavelength. By examining statistical correlations in this data, the interdependence of the fractions of constituent binary compounds, together with the associated changes in emission characteristics, can be clarified without the need to grow a systematic series of samples

One-Dimensional ZnO/Gold Junction for Simultaneous and Versatile Multisensing Measurements

The sensing capabilities of zinc oxide nano/micro-structures have been widely investigated and these structures are frequently used in the fabrication of cutting-edge sensors. However, to date, little attention has been paid to the multi-sensing abilities of this material. In this work, we present an efficient multisensor based on a single zinc oxide microwire/gold junction. The device is able to detect in real time three different stimuli, UV-VIS light, temperature and pH variations. This is thanks to three properties of zinc oxide its photoconductive response, pyroelectricity and surface functionalization with amino-propyl groups, respectively. The three stimuli can be detected either simultaneously or in a sequence/random order. A specific mathematical tool was also developed, together with a design of experiments (DoE), to predict the performances of the sensor. Our micro-device allows reliable and versatile real-time measurements of UV-VIS light, temperature and pH variations. Therefore, it shows great potential for use in the field of sensing for living cell cultures

the effects of the film thickness and roughness in the anodization process of very thin aluminum films

Introduction The anodization of aluminum foils having micrometer thickness is a common process and results in hexagonally self-ordered alumina membranes. However, anodic aluminum oxide (AAO) membranes fabricated from nanometer-thin films present new challenges to the anodization process, since aluminum films adheres poorly on supporting substrates and the smoothness of the film is highly related to the kind of substrate. In the current work we studied the effect of the aluminum thickness and roughness, using films ranging from 100 to 800 nm in thickness and from 2 to 15 nm in root means square roughness (on a scan area of 100 μm2), on the final alumina morphology. We deposited Al thin films by sputtering method on transparent conductive glass substrates. A strong dependence between the Al film roughness and the final alumina pore organization was observed. It was also determined that by reducing the Al film thickness, smaller Al grains were generated, leading to a homogenous pore formation. It was found that, for thicknesses below 300 nm, the electrolyte used to perform anodization becomes a critical parameter due to the competitive effect of aluminum delamination with respect to the anodization reaction. Phosphoric acid showed less delamination problems than oxalic acid

In situ generation of silver nanoparticles in PVDF for the development of resistive switching devices

It is widely accepted that resistive switching devices (RSDs) are extremely appealing as active components in computer memories and logic gates in electronics, directly enabling neuromorphic functionalities. The aim of this study is to investigate the chemical and electrical properties of a nanocomposite polymer, the active component of the device, in order to characterise its composition and behaviour under electric field. This paper presents the morphological and chemical characterization of an in-situ generated silver – Polyvinylidene fluoride-hexafluoropropylene PVDF-HFP nanocomposite (NC) material. A silver salt is added as precursor to the polymer solution and then, after a film casting step, the nanoparticles generation and growth processes are carried out by way of UV irradiation; the growth and the distribution of in-situ generated silver nanoparticles (NPs) in the polymer matrix are described. The devices, built on a planar electrode structure, undergo an I/V test to explore their resistance states at different switching voltages. Furthermore, after electrical analysis a remarkable R off /R on ratio and a relatively low switching voltage (3 V) are achieved, demonstrating the suitability of the developed material for the next generation of soft, wearable, RSDs