A5007319638- GaN-based semiconductor devices and materials
- Nanowire Synthesis and Applications
- Semiconductor materials and devices
- Semiconductor Quantum Structures and Devices
- Ga2O3 and related materials
- ZnO doping and properties
- Photonic and Optical Devices
- Semiconductor Lasers and Optical Devices
- Photonic Crystals and Applications
- Metal and Thin Film Mechanics
- Electronic and Structural Properties of Oxides
- Advancements in Semiconductor Devices and Circuit Design
- Advanced Chemical Physics Studies
- Molecular Junctions and Nanostructures
- Silicon Nanostructures and Photoluminescence
- Semiconductor materials and interfaces
- Plasma Diagnostics and Applications
- Photocathodes and Microchannel Plates
- Acoustic Wave Resonator Technologies
- Metamaterials and Metasurfaces Applications
- Anodic Oxide Films and Nanostructures
- Advanced Electron Microscopy Techniques and Applications
- Plasmonic and Surface Plasmon Research
- Mechanical and Optical Resonators
- 2D Materials and Applications
Sandia National Laboratories
2015-2024
University of British Columbia
2024
Sandia National Laboratories California
2011-2021
Radiology Associates of Albuquerque
2008-2016
Center for Integrated Nanotechnologies
2009-2014
National Technical Information Service
2006-2012
Office of Scientific and Technical Information
2006-2012
Xidian University
2012
McGill University
2012
Naval Postgraduate School
2011
Solid‐state lighting has made tremendous progress this past decade, with the potential to make much more over coming decade. In article, current status of solid‐state relative its ultimate be “smart” and ultra‐efficient is reviewed. Smart, would enable both very high “effective” efficiencies potentially large increases in human performance. To achieve ultra‐efficiency, phosphors must give way multi‐color semiconductor electroluminescence: some technological challenges associated such...
Light-emitting sources and devices permeate every aspect of our lives are used in lighting, communications, transportation, computing, medicine. Advances multifunctional "smart lighting" would require revolutionary concepts the control emission spectra directionality. Such might be possible with new schemes regimes light–matter interaction paired developments light-emitting materials. Here we show that all-dielectric metasurfaces made from III–V semiconductors embedded emitters have...
Vertically aligned InGaN/GaN nanorod light emitting diode (LED) arrays were created from planar LED structures using a new top-down fabrication technique consisting of plasma etch followed by an anisotropic wet etch. The results in straight, smooth, well-faceted nanorods with controllable diameters and removes the damage. 94% LEDs are dislocation-free reduced quantum confined Stark effect is observed due to piezoelectric fields. Despite these advantages, IQE measured photoluminescence...
We report the growth of exceptionally well aligned and vertically oriented GaN nanowires on r-plane sapphire wafers via metal–organic chemical vapour deposition. The were grown without use either a template or patterning. Transmission electron microscopy indicates are single crystalline, free threading dislocations, have triangular cross-sections. high degree vertical alignment is explained by crystallographic match between surface. find that size uniformity highly dependent nickel nitrate...
We demonstrate stable, single-frequency output from single, as-fabricated GaN nanowire lasers operating far above lasing threshold. Each laser is a linear, double-facet functioning as gain medium and optical resonator, fabricated by top-down technique that exploits tunable dry etch plus anisotropic wet for precise control of the dimensions high material gain. A single-mode linewidth ~0.12 nm >18 dB side-mode suppression ratio are measured. Numerical simulations indicate arises strong mode...
Nonpolar and semipolar III-nitride-based blue green light-emitting diodes (LEDs) have been extensively investigated as potential replacements for current polar c-plane LEDs. High-power low-efficiency-droop LEDs demonstrated on nonpolar planes III-nitride due to the advantages of eliminated or reduced polarization-related electric field homoepitaxial growth. Semipolar (202¯1) (202¯1¯) contributed bridging "green gap" (low efficiency in spectral region) by incorporating high indium...
We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core–shell single-nanowire lasers by optical pumping at room temperature. The nanowire were fabricated using a hybrid approach consisting of top-down two-step etch process followed bottom-up regrowth process, enabling precise geometrical control and high material gain confinement. modal spectra the curves measured micro-photoluminescence analyzed Hakki-Paoli method. Significantly lower thresholds due to compared previously...
The concept of proton affinity on semiconductor surfaces has been explored through an investigation the chemistry amines Ge(100)-2 x 1, Si(100)-2 and C(100)-2 1 surfaces. Multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy, temperature programmed desorption (TPD), density functional theory (DFT) calculations were used in studies. We find that methylamine, dimethylamine, trimethylamine undergo molecular chemisorption surface formation Ge-N dative bonds. In...
The spatial distribution of defect-related and band-edge luminescence from GaN nanowires grown by metal−organic chemical vapor deposition was studied spatially resolved cathodoluminescence imaging spectroscopy. A surface layer exhibiting strong yellow (YL) near 566 nm in the revealed, compared to weak YL bulk. In contrast, other 428 (blue luminescence) 734 (red luminescence), addition (BEL) at 366 nm, were observed bulk but largely absent surface. As nanowire width approaches a critical...
We have investigated the correlated surface electronic and optical properties of [0001]-oriented epitaxial InN nanowires grown directly on silicon. By dramatically improving growth process, we achieved, for first time, intrinsic both within bulk at nonpolar surfaces. The near-surface Fermi-level was measured to be ∼0.55 eV above valence band maximum undoped nanowires, suggesting absence electron accumulation pinning. This result is in direct contrast problematic degenerate two-dimensional...
Correlated atom probe tomography, cross-sectional scanning transmission electron microscopy, and cathodoluminescence spectroscopy are used to analyze InGaN/GaN multiquantum wells (QWs) in nanowire array light-emitting diodes (LEDs). Tomographic analysis of the In distribution, interface morphology, dopant clustering reveals material quality comparable that planar LED QWs. The position-dependent CL emission wavelength nonpolar side-facet QWs semipolar top is correlated with composition.
A solar cell based on a hybrid nanowire–film architecture consisting of vertically aligned array InGaN/GaN multi-quantum well core–shell nanowires which are electrically connected by coalesced p-InGaN canopy layer is demonstrated. This unique structure allows for standard planar device processing, solving key challenge with nanowire integration, while enabling various advantages the absorbing region such as higher indium composition InGaN layers elastic strain relief, more efficient carrier...
The optical properties, indium concentration and distribution, defect morphology, strain distribution of GaN/InGaN coaxial nanowires grown by metal organic chemical vapor deposition were investigated using spatially resolved cathodoluminescence, scanning transmission electron microscopy, finite element analysis. results indicate that InGaN layers with 40% or greater incorporation low density can be achieved. in the shell layer was measured qualitatively correlated calculated distribution....
The electronic properties of heterojunction electron gases formed in GaN/AlGaN core/shell nanowires with hexagonal and triangular cross sections are studied theoretically. We show that at nanoscale dimensions, the nonpolar system exhibits degenerate quasi-one-dimensional hexagon corners, which transition to a core-centered gas lower doping. In contrast, polar either nondegenerate on face or single corner opposite face, depending termination face. More generally, our results indicate closed...
GaN-InGaN core-shell nanowire array devices are characterized by spectrally resolved scanning photocurrent microscopy (SPCM). The spatially external quantum efficiency is correlated with structure and composition inferred from atomic force microscope (AFM) topography, transmission electron (STEM) imaging, Raman microspectroscopy, (SPCM) maps of the effective absorption edge. experimental analyses coupled finite difference time domain simulations to provide mechanistic understanding spatial...
Voltage-controlled room temperature isothermal reversible spin crossover switching of [Fe{H2B(pz)2}2(bipy)] thin films is demonstrated. This evident in film bilayer structures where the molecular adjacent to a ferroelectric. The ferroelectric, either polyvinylidene fluoride hexafluoropropylene or croconic acid (C5H2O5), appears lock complex largely low high state depending on direction ferroelectric polarization. In both planar two terminal diode structure and transistor structure, voltage...
Abstract We have observed the z = 4.3 protocluster SPT2349−56 with Australia Telescope Compact Array (ATCA) aim of detecting radio-loud active galactic nuclei (AGNs) among ∼30 submillimeter (submm) galaxies (SMGs) identified in structure. detect central complex submm sources at 2.2 GHz a luminosity L (4.42 ± 0.56) × 10 25 W Hz −1 . MeerKAT and Australian Square Kilometre Pathfinder also source 816 MHz 888 MHz, respectively, constraining radio spectral index to α −1.45 0.16, implying 1.4,rest...
We have investigated the room temperature adsorption of methylamine, dimethylamine and trimethylamine using density functional theory (DFT) multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy. It was found that reaction pathways amines resemble precursor-mediated dissociative chemisorption ammonia. Our calculations showed although dissociation involving N–C bond cleavage is thermodynamically more favorable than N–H pathway, activation barrier for N–CH3...
Thermal transport and breakdown in Joule-heated GaN nanowires is investigated using a combination of microphotoluminescence situ TEM characterization. The thermal conductivity the estimated to be <80 W/m·K, which substantially below bulk value. Catastrophic individual observed occur at maximum temperature approximately 1000 K, nanowire morphology near region indicates that failure occurs via decomposition, conclusion validated by images obtained during process.
The deformation, fracture mechanisms, and the strength of individual GaN nanowires were measured in real time using a transmission electron microscope−scanning probe microscope (TEM-SPM) platform. Surface mediated plasticity, such as dislocation nucleation from free surface plastic deformation between SPM (the punch) nanowire contact observed situ. Although local plasticity was frequently, global not observed, indicating overall brittle nature this material. Dislocation propagation is...
GaN nanowires oriented along the nonpolar a-axis were analyzed using pulsed laser atom probe tomography (APT). Stoichiometric mass spectra achieved by optimizing temperature, applied dc voltage, and pulse energy. Local variations in measured stoichiometry observed correlated with facet polarity scanning electron microscopy. Fewer N atoms detected from Ga-polar surfaces due to uncorrelated evaporation of N2 ions following adatom diffusion. The differences Ga ion behaviors are considered...
Stable single-mode lasing operation from a pair of coupled GaN nanowires is demonstrated through optical pumping. with different lengths were placed side-by-side in contact to form cavity nanoprobe manipulation. Unlike individual nanowire lasers, which operate combined multiple transverse and longitude mode oscillation, nanowire-pair provides selection mechanism the Vernier effect, can strongly enhance free spectrum range between adjacent resonant modes generate stable high side-mode...
Emerging applications such as solid-state lighting and display technologies require micro-scale vertically emitting lasers with controllable distinct lasing wavelengths broad wavelength tunability arranged in desired geometrical patterns to form "super-pixels". Conventional edge-emitting current surface-emitting that abrupt changes semiconductor bandgaps or cavity length are not a viable solution. Here, we successfully address these challenges by introducing new paradigm extends the laser...
Nonvolatile, molecular multiferroic devices have now been demonstrated, but it is worth giving some consideration to the issue of whether such could be a competitive alternative for solid-state nonvolatile memory. For Fe (II) spin crossover complex [Fe{H2B(pz)2}2(bipy)], where pz = tris(pyrazol-1-yl)-borohydride and bipy 2,2′-bipyridine, voltage-controlled isothermal changes in electronic structure state demonstrated are accompanied by conductance. Higher conductance seen with...