A5073588917- GaN-based semiconductor devices and materials
- Ga2O3 and related materials
- Semiconductor materials and devices
- ZnO doping and properties
- Electronic and Structural Properties of Oxides
- Innovation Policy and R&D
- Metal and Thin Film Mechanics
- Private Equity and Venture Capital
- State Capitalism and Financial Governance
- Nanowire Synthesis and Applications
- Surface and Thin Film Phenomena
- Capital Investment and Risk Analysis
- Machine Learning in Materials Science
- Magnetic and transport properties of perovskites and related materials
- Plasmonic and Surface Plasmon Research
- Molecular Junctions and Nanostructures
- Force Microscopy Techniques and Applications
North Carolina State University
2011-2019
Clean Energy (United States)
2016-2017
HexaTech (United States)
2014
Tokyo University of Agriculture and Technology
2014
Tokuyama (Japan)
2014
Single crystal AlN provides a native substrate for Al-rich AlGaN that is needed the development of efficient deep ultraviolet light emitting and laser diodes. An absorption band centered around 4.7 eV (∼265 nm) with an coefficient above 1000 cm−1 observed in these substrates. Based on density functional theory calculations, substitutional carbon nitrogen site introduces at this energy. A series single crystalline wafers were used to demonstrate linearly increased carbon, strongly supporting...
Controllable n-type doping over wide ranges of carrier concentrations in AlN, or Al-rich AlGaN, is critical to realizing next-generation applications high-power electronics and deep UV light sources. Silicon not a hydrogenic donor AlN as it GaN; despite this, the concentration should be controllable, albeit less efficiently, by increasing during growth. At low levels, an increase Si content leads commensurate free electrons. Problematically, this trend does persist higher levels. In fact,...
In order to understand the influence of dislocations on doping and compensation in Al-rich AlGaN, thin films were grown by metal organic chemical vapor deposition (MOCVD) different templates sapphire low dislocation density single crystalline AlN. AlGaN AlN exhibited highest conductivity, carrier concentration, mobility for any concentration due threading related reduced self-compensation. The onset self-compensation, i.e., “knee behavior” was found depend only potential silicon, strongly...
A prominent 2.8 eV emission peak is identified in bulk AlN substrates grown by physical vapor transport. This shown to be related the carbon concentration samples. Density functional theory calculations predict that this caused a donor-acceptor pair (DAP) recombination between substitutional on nitrogen site and vacancy. Photoluminescence photoluminescence-excitation spectroscopy are used confirm model indicate DAP character of emission. The interaction defects provides pathway creating...
Co-doping AlN crystals with Si is found to suppress the unwanted 4.7 eV (265 nm) deep ultraviolet absorption associated isolated carbon acceptors common in materials grown by physical vapor transport. Density functional theory calculations hybrid functionals demonstrate that silicon forms a stable nearest-neighbor defect complex carbon. This predicted absorb at 5.5 and emit or above 4.3 eV. Absorption photoluminescence measurements of co-doped samples confirm presence CN-SiAl emission peaks...
A Fermi-level control scheme for point defect management using above-bandgap UV illumination during growth is presented. We propose an extension to the analogy between Fermi level and electrochemical potential such that of a charged in material with steady-state populations free charge carriers may be expressed terms quasi-Fermi levels. series highly Si-doped Al0.65Ga0.35N films grown by metalorganic chemical vapor deposition without showed samples under had increased carrier concentration,...
Venture capital (VC) firms spent over $25 billion funding clean energy technology (cleantech) start-ups from 2006 to 2011. Less than half of that was returned; as a result, has dried up in the cleantech sector. But International Energy Agency warns, without new technologies, world cannot cost-effectively confront climate change. In this article, we present most comprehensive account date VC boom and bust, aggregating hundreds investments calculate risk return profile cleantech, compared with...
Property coupling at interfaces between active materials is a rich source of functionality, if defect densities are low, smooth and the microstructure featureless. Conventional synthesis techniques generally fail to achieve this when have highly dissimilar structure, symmetry bond type-precisely potential for property engineering most pronounced. Here we present general methodology, involving systematic control chemical boundary conditions in situ, by which crystal habit, thus growth mode,...
The formation energies of oxygen and silicon impurities have been examined explicitly in ${\mathrm{Al}}_{0.65}{\mathrm{Ga}}_{0.35}\mathrm{N}$ using hybrid exchange-correlation density-functional theory simulations. Both were initialized on-site substitutional off-site DX configurations a range charge states. ${\mathrm{O}}_{\mathrm{N}}^{+1}$ donor was found to always relax into an configuration, its energy is relatively independent local chemistry (the configuration Al Ga atoms surrounding...
Interfaces between dissimilar polar materials may provide a pathway to new device functionality, including high carrier mobility layers at the interface. The development of these has proven challenging, in part because energy cost forming surfaces. Our density functional theory calculations explore mechanisms by which real material satisfies electrostatic criteria for stability imposed surface. consequences polarity are studied comparing formation energies, charge distribution, and...
Smooth, commensurate alloys of ⟨111⟩-oriented Mg0.52Ca0.48O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These unique examples coherent cubic oxide|nitride interfaces with structural morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated n-type GaN. A comparison leakage current density for conventional growth reveals a nearly 100× reduction in the samples....
One of the main limitations based on point defects in AlN is related to UV absorption band present at 265 nm. This relatively broad limits use bulk substrates within deep range and several complicated fabrication procedures have been devised overcome this limitation. The origin for along with corresponding photoluminescence signatures will be reviewed. C N - V + were identified as directly associated 4.7 eV emission 2.8 eV. due a transition between state conduction band, while arises from...
Ohmic RF-MEMS switches hold much promise for low power wireless communication, but long-term degradation currently plagues their reliable use. Failure in these devices occurs at the contact and is complicated by fact that same asperities bear mechanical load are also important to flow of electrical current needed signal processing. Materials selection holds key overcoming barriers prevent widespread Current efforts materials have been based on material's (or alloy's) ability resist oxidation...
AlGaN alloys are the building blocks for deep UV optoelectronics and high-power devices. It has been demonstrated that highest crystalline quality films with high Al content obtained on AlN single crystal substrates. The resulting mismatch between causes a compressive strain within layers, which varies composition. Nevertheless, pseudomorphic higher than 50%, dislocation densities lower 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup>...
AlGaN alloys are the building blocks for deep UV optoelectronics and high-power devices. It has been demonstrated that highest crystalline quality films with high Al content obtained on AlN single crystal substrates. The resulting mismatch between causes a compressive strain within layers, which varies composition. Nevertheless, pseudomorphic higher than 50%, dislocation densities lower 10 4 cm -2 have achieved, sustaining stresses thicknesses exceeding 3 µm. Such results demonstrate...