A5026069029- ZnO doping and properties
- Ga2O3 and related materials
- GaN-based semiconductor devices and materials
- Semiconductor materials and devices
- Metal and Thin Film Mechanics
- Copper-based nanomaterials and applications
- Machine Learning in Materials Science
- Electronic and Structural Properties of Oxides
- Semiconductor materials and interfaces
- Semiconductor Quantum Structures and Devices
- Chalcogenide Semiconductor Thin Films
- Gas Sensing Nanomaterials and Sensors
- Ion-surface interactions and analysis
- Engineering and Technology Innovations
- Boron and Carbon Nanomaterials Research
- Electron and X-Ray Spectroscopy Techniques
- Integrated Circuits and Semiconductor Failure Analysis
- Nanowire Synthesis and Applications
- Metallurgical and Alloy Processes
- Experimental Learning in Engineering
- Inorganic Chemistry and Materials
- Photonic and Optical Devices
- Terahertz technology and applications
- Quantum Dots Synthesis And Properties
- MXene and MAX Phase Materials
University of Hawaiʻi at Mānoa
2024-2025
Western Michigan University
2015-2024
American Society For Engineering Education
2024
University of Hawaii System
2024
University of Canterbury
2007-2020
MacDiarmid Institute for Advanced Materials and Nanotechnology
2007-2020
University at Buffalo, State University of New York
2010-2016
University of Michigan
2016
Buffalo State University
2012-2013
New York University
2010
Ni, Ir, Pd, Pt, and silver oxide Schottky contacts were fabricated on the Zn-polar face of hydrothermally grown, bulk ZnO. A relationship was found between barrier height contact free energy formation its “metal” oxide. This is consistent with dominating influence oxygen vacancies (VO) which tend to pin ZnO Fermi level close VO (+2,0) defect at approximately 0.7eV below conduction band minimum. Therefore, a key goal in fabrication high quality should be minimization near metal-ZnO interface.
Results are reported for four Nb-Ta single-crystal superlattices with 50 AA wavelength grown simultaneously on chosen substrates such that the crystal growth and superlattice structure take (100), (110), (111) (211) orientations in respective cases.
A method of fabricating highly rectifying Schottky contacts on n-type ZnO using silver oxide has been developed and used to compare diode performance hydrothermal melt grown, bulk, single crystals. Silver diodes have lower ideality factors, reverse current voltage dependence, higher series resistance, larger surface-polarity related differences in barrier height, compared those ZnO. These effects are explained by the large difference resistivity between Barrier heights 1.20eV were achieved...
We examine ZnSnN2, a member of the class materials contemporarily termed “earth-abundant element semiconductors,” with an emphasis on evaluating its suitability for photovoltaic applications. It is predicted to crystallize in orthorhombic lattice energy gap 2 eV. Instead, using molecular beam epitaxy deposit high-purity, single crystal as well highly textured polycrystalline thin films, only monoclinic structure observed experimentally. Far from being detrimental, we demonstrate that cation...
The band gap of earth-abundant ZnSnN2 can be tuned between 1 and 2 eV by varying the growth conditions resulting cation disorder. optical absorption edges carrier densities fall model curves for cation-ordered orthorhombic disordered wurtzite ZnSnN2. Hard X-ray photoemission spectra suggest different degrees disorder from comparison with hybrid DFT-calculated states. Semiconductor material systems tunable gaps are great interest a variety optoelectronic applications, including solid state...
Planar Pd, Pt, Au, and Ag Schottky diodes with low ideality factors were fabricated on the Zn-polar (0001) O-polar (0001¯) faces of bulk, single crystal ZnO wafers. The characterized by current-voltage capacitance-voltage measurements. A polarity effect was observed for Pt Pd higher quality barriers achieved face. No significant Au or diodes. highest as metal barrier heights varying between 0.77 1.02eV. This is possibly due to degrees oxidation contacts.
The authors report the successful growth of almost perfect single crystal superlattices made from alternating layers Nb and Ta with superlattice periodicities in range 20-1000 AA.
High-resolution x-ray photoemission spectroscopy measurements are used to determine the valence band offset of wurtzite-InN/GaN(0001) heterojunctions be $0.58\ifmmode\pm\else\textpm\fi{}0.08\text{ }\text{eV}$. This is discussed within context previous and calculations in agreement with value $0.52\ifmmode\pm\else\textpm\fi{}0.14\text{ }\text{eV}$ determined from alignment experimentally charge neutrality levels InN GaN. The heterojunction forms type-I straddling configuration a conduction...
Magnetotransport measurements and x-ray photoemission spectroscopy were used to investigate the surface conductivity of ZnO. Near-surface downward band bending, consistent with electron accumulation, was found on polar nonpolar faces bulk ZnO single crystals. A significant polarity effect observed in that bending consistently stronger Zn-polar face weaker O-polar face. The accumulation layer significantly influence electrical properties high resistivity, hydrothermally grown crystals at...
Variable magnetic field Hall effect, photoluminescence, and capacitance-voltage (CV) analysis have been used to study InN layers grown by plasma assisted molecular beam epitaxy. All three techniques reveal evidence of a buried p-type layer beneath surface electron accumulation in heavily Mg-doped samples. Early indications suggest the Mg acceptor level may lie near 110meV above valence band maximum. The development doping offers great promise for future based devices.
Hall effect, photoluminescence, and Schottky diode measurements were made on the Zn-polar O-polar faces of undoped, bulk, single crystal, c-axis ZnO wafers. Significant polarity related differences observed in PL characteristics low carrier concentration, hydrothermally grown Increased emission from free exciton recombinations between 3.3725 3.3750eV was face. Conversely, 3.3640 3.3680eV more intense The barrier heights silver oxide diodes approximately 130meV larger face compared to
Soft x-ray emission and absorption spectroscopy of the $\text{O}\text{ }K$-edge are employed to investigate electronic structure wurtzite ZnO(0001). A quasiparticle band calculated within $GW$ approximation agrees well with data, most notably energetic location $\text{Zn}\text{ }3d--\text{O}\text{ }2p$ hybridized state anisotropy spectra. Dispersion in is mapped using coherent $\mathbf{k}$-selective part resonant We show that a more extensive mapping bands possible case crystalline such as found ZnO.
Epitaxial gadolinium nitride films with well-oriented crystallites of up to 30 nm have been grown on yttria-stabilized ziconia substrates using a plasma-assisted pulsed laser deposition technique. We observe that the epitaxial GdN growth proceeds top oxide buffer layer forms via reaction between deposited Gd and mobile oxygen from substrate. Hall effect measurements show are electron doped degeneracy, carrier concentrations 4×1020 cm−3. Magnetic establish TC 70 K coercive field can be tuned...
Deliberately oxidized iridium, platinum, and palladium Schottky contacts were fabricated on the Zn-polar O-polar faces of hydrothermal bulk ZnO by eclipse pulsed laser deposition in an oxygen ambient. The barrier heights these significantly higher than their plain metal counterparts, with ideality factors approaching image-force-controlled limit for laterally homogeneous interfaces. key aspects this technique are a low energy use oxidizing environment which reduces interfacial defects,...
Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) synchrotron radiation (150 to 1486 eV). In particular, from lowest binding energy states was found be significantly more intense on Zn-polar face compared O-polar face. This is a consistent effect that can used as simple, nondestructive indicator crystallographic...
We present evidence, from theory and experiment, that ZnSnN_{2} MgSnN_{2} can be used to match the band gap of InGaN without alloying-by exploiting cation disorder in a controlled fashion. base this on determination S, long-range order parameter sublattice, for series epitaxial thin films using three different techniques: x-ray diffraction, Raman spectroscopy, situ electron diffraction. observe linear relationship between S^{2} optical both (1.12-1.98 eV) (1.87-3.43 eV). The results clearly...
The surfaces of In- and N-polarity InN grown by molecular-beam epitaxy have been investigated using core-level valence band x-ray photoemission spectroscopy (XPS). From the ratio In N XPS signal intensities, clean found to be terminated adlayers, in agreement with predictions previous first-principles calculations. are $\ensuremath{\sim}3.4$ $\ensuremath{\sim}2.0\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$ In, each case 1 ML more than for Ga on GaN under metal-rich growth conditions. indicates a...
The rectifying performance of platinum, palladium, and iridium Schottky contacts on ZnO(0001) surfaces was dramatically improved by their deliberate in-situ oxidation using an O2:Ar rf plasma during fabrication. For example, oxidized Pt exhibited current rectification 12 orders-of-magnitude, effective barrier heights up to 1.30 eV, stable high-temperature operation at 180 °C, compared the ohmic behavior (i.e., zero rectification/barrier height) unoxidized contacts. Oxidized Pd Ir also showed...
We report on the crystal structure of epitaxial ZnSnN2 films synthesized via plasma-assisted vapor deposition (111) yttria stabilized zirconia (YSZ) and (001) lithium gallate (LiGaO2) substrates. X-ray diffraction measurements performed deposited LiGaO2 substrates show evidence single-crystal, phase-pure orthorhombic in Pn21a symmetry [space group (33)], with lattice parameters good agreement theoretically predicted values. This is imposed by substrate, which also has symmetry. A structural...
Very high temperature operation β-Ga2O3 Schottky contacts were fabricated on moderately doped 2¯01 single crystal substrates using four different types of intentionally oxidized platinum group metal (PGM) (SCs), i.e., PtOx, IrOx, PdOx, and RuOx (x ∼ 2.0, 2.2, 1.1, 2.4, respectively) formed by reactive rf sputtering plain-metal targets in an oxidizing plasma. All PGM SCs showed rectification ratios (at ± 3 V) more than 10 orders magnitude up to 300 °C, with almost no measurable increase...
Hydrothermally grown bulk ZnO (Tokyo Denpa) was investigated using junction-capacitance spectroscopy on silver oxide Schottky contacts (barrier height of 1.20eV, ideality factor 1.04). Two main shallow defects, T1 and T2, with thermal activation energies 13 52meV, respectively, were identified. closely lying, deep defect levels E3∕E3′ at approximately 320meV below the conduction band found in higher concentrations (mid-1014cm−3) than donors. 4K photoluminescence showed dominant emission from...