A5043619375- Silicon Carbide Semiconductor Technologies
- Semiconductor materials and devices
- Graphene research and applications
- Silicon and Solar Cell Technologies
- GaN-based semiconductor devices and materials
- Chalcogenide Semiconductor Thin Films
- Advanced Semiconductor Detectors and Materials
- Copper Interconnects and Reliability
- Semiconductor Quantum Structures and Devices
- Thin-Film Transistor Technologies
- Diamond and Carbon-based Materials Research
- Ga2O3 and related materials
- Quantum Dots Synthesis And Properties
- Metal and Thin Film Mechanics
- Advanced Optical Sensing Technologies
- Solid State Laser Technologies
- Semiconductor materials and interfaces
- Integrated Circuits and Semiconductor Failure Analysis
- Carbon Nanotubes in Composites
- Advanced Fiber Laser Technologies
- Quantum and electron transport phenomena
- ZnO doping and properties
- Ocular and Laser Science Research
- Perovskite Materials and Applications
- 2D Materials and Applications
DEVCOM Army Research Laboratory
2013-2024
United States Army Combat Capabilities Development Command
2023-2024
University of Virginia
2019
United States Naval Research Laboratory
2007-2011
United States Navy
2007-2011
Amethyst Technologies (United States)
2011
Amethyst Research (United States)
2010
Amethyst Research (United Kingdom)
2009
Pennsylvania State University
2009
West Virginia University
2000-2008
We report dc and the first-ever measured small-signal radio-frequency (RF) performance of epitaxial-graphene RF field-effect transistors (FETs), where layer is formed by graphitization 2-in-diameter Si-face semi-insulating 6H-SiC (0001) substrates. The gate processed with a metal on top high-k Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dielectric deposited via an...
We report a direct correlation between carrier mobility and Raman topography of epitaxial graphene (EG) grown on silicon carbide (SiC). show the Hall material Si-face SiC [SiC(0001)] is not only highly dependent thickness uniformity but also monolayer strain uniformity. Only when both are uniform over significant fraction (> 40%) device active area does exceed 1000 cm2/V-s. Additionally, we achieve high (18,100 cm2/V-s at room temperature) C-face [SiC(000-1)] that depends strongly layer...
Epitaxial graphene (EG) films were grown in vacuo by silicon sublimation from the (0001) and (0001¯) faces of 4H-SiC 6H-SiC. Hall effect mobilities sheet carrier densities measured at 300 77 K data depended on growth face. About 40% samples exhibited holes as dominant carrier, independent Generally, increased with decreasing density, type substrate polytype. The contributions scattering mechanisms to conductivities are discussed. results suggest that for near-intrinsic epitaxial will be ∼150...
In this letter, we present state-of-the-art performance of top-gated graphene n-FETs and p-FETs fabricated with epitaxial layers grown on Si-face 6H-SiC substrates 50-mm wafers. The current-voltage characteristics these devices show excellent saturation on-state current densities (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) 0.59 A/mm at V xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> = 1 1.65 3 V. I /I...
We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-infrared magneto transmission (FIR-MT), and atomic force microscopy (AFM) results from graphene films produced by radiative heating in an ultrahigh vacuum (UHV) chamber or radio frequency (RF) furnace annealing a high chemical vapor deposition system on Si- C-face 4H SiC substrates at 1200−1600 °C. Although the level methods are different, two chemically similar with RF typically producing thicker...
The paths of basal plane dislocations (BPDs) through 4H-SiC epitaxial layers grown on wafers with an 8° offcut were tracked using ultraviolet photoluminescence imaging. reduction BPDs by conversion to threading edge was investigated at ex situ and in growth interrupts. For interrupts, are imaged after each several growths. wafer remains the reactor for interrupts is finished. a combination temperature, propane flow, duration has been determined, which achieve BPD 98%.
The dominant recombination processes controlling the carrier lifetime in n-type 4H–SiC epitaxial layers grown with low concentrations of Z1/2 defect (the bulk killer), where no longer determines lifetime, have been investigated by studying variation temperature. temperature dependent lifetimes were obtained primarily low-injection photoluminescence decay for several low-Z1/2 epilayers over a wide range. results fitted to simulations rate, bulk, surface and interface was considered. No...
Epitaxial layers were grown on 4° off-axis 4H-SiC substrates by hot-wall chemical vapor deposition. The reduced off-cut angle resulted in lower basal plane dislocation (BPD) densities. dependence of BPD reduction growth conditions was investigated using ultraviolet photoluminescence (UVPL) imaging. With this method, it found that the dislocations converting to threading edge throughout thickness film. A high (≥ 97%) conversion efficiency for all films with orientation. 100% achieved several...
Local recombination properties of threading screw and edge dislocations in 4H–SiC epitaxial layers have been studied using electron beam induced current (EBIC). The minority carrier diffusion length the vicinity was found to vary with dislocation type. Screw had a more pronounced impact on than dislocations, evidencing stronger activity. Temperature dependence EBIC contrast suggests that their activity is controlled by deep energy levels cores. This paper shows type (screw or edge) can be...
In situ growth interrupts were executed during the of 8° off-cut 4H-SiC epitaxial layers to determine dependence efficiency for converting basal plane dislocations (BPDs) threading edge (TEDs) on interrupt temperature. Three samples grown with 15min near middle a 30–40μm thick, n-type doped layer at 1400, 1500, and 1580°C. Ultraviolet photoluminescence (UVPL) mapping these reveals BPDs permits observation how defects extend into through epilayer. From lateral length in UVPL wafer map, it was...
This paper reports on a 4H-SiC single-photon avalanche diode (SPAD) operating at UV wavelengths of 280 and 350 nm. The SPAD shows low dark currents 20 57 fA 80 V 90% breakdown voltage, respectively. quantum efficiency (QE) reaches its peak 43% 270 nm is < 0.007% 400 nm, indicating high UV-to-visible rejection ratio > 6100. fast self-quenching photon count rate 1.44 MHz in the passive-quenching mode. At wavelength detection (SPDE) 2.83 % with 22 kHz achieved reverse bias 116.8 V. SPDE lower,...
An in vacuo thermal desorption process has been accomplished to form epitaxial graphene (EG) on 4H- and 6H-SiC substrates using a commercial chemical vapor deposition reactor. Correlation of growth conditions the morphology electrical properties EG are described. Raman spectra Si-face samples were dominated by monolayer thickness. This approach was used grow 50 mm SiC wafers that subsequently fabricated into field effect transistors with fmax 14 GHz.
Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H- 6H-SiC substrates. The process was performed under high vacuum (<10-4 mbar) in a commercial chemical vapor deposition SiC reactor. A method for H2 etching the on-axis sub-strates developed to produce surface steps with heights 0.5 nm Si-face 1.0 1.5 C-face each polytype. form graphene substrates immediately after Raman spectroscopy these samples confirmed formation graphene. morphology is described. For...
Graphene was epitaxially grown on both the C- and Si-faces of 4H- 6H-SiC(0001) under an argon atmosphere high vacuum conditions. Following growth, samples were imaged with Nomarski interference contrast atomic force microscopies it found that growth led to improved morphologies C-face films but Si-face not significantly affected. Free carrier transport studies conducted through Hall effect measurements, mobilities increase sheet densities decrease for those as compared The concurrent...
The temperature used for growth of GaN by molecular beam epitaxy is ultimately limited the greatly reduced rate related to thermal decomposition. This limiting apparently varies from group group. Factors influencing decomposition are species (atomic versus metastable nitrogen), surface polarity (N- Ga-polar), presence atomic hydrogen, and varying Ga-overpressure. Surface predominant influence determining onset There indications that use a significant Ga-overpressure can suppress allowing an...
A novel taper-doping anode termination method is introduced for high-voltage silicon carbide devices. The employs a subresolution two-tone mask to achieve gray-scale exposure and smoothly tapered photoresist profile. Using the profile as an implantation mask, self-aligned 6-kV SiC PiN diodes are demonstrated with 90% of parallel-plate breakdown voltage. avalanche design controlled reversible. This one-step technique allows wide control over width shape has device material applicability.
The effect of surface polarity on InN growth GaN by metalorganic chemical vapor deposition (MOCVD) was investigated. the found to follow that initial template as determined a comparison experimental and simulated convergent beam electron diffraction patterns. Under identical MOCVD conditions, In-polar observed nucleate grow Ga-polar pyramidal-shaped islands with (101¯1) stable facet. In contrast, enhanced lateral reduced roughness were for N-polar grown GaN. films (0001) sapphire substrates...
A heterojunction between thin films of nanocrystalline diamond (NCD) and 4H-SiC has been developed. Undoped B-doped NCDs were deposited on both n− p− SiC epilayers. I-V measurements p+ NCD∕n− indicated Schottky rectifying behavior with a turn-on voltage around 0.2V. The current increased over eight orders magnitude an ideality factor 1.17 at 30°C. Ideal energy-band diagrams suggested possible conduction mechanism for electron transport from the band to either valence or acceptor level NCD...
Silicon carbide Schottky diodes with thick i-regions are reported. Compared previously reported p-i-n photodiodes, a shift of the absorption peak from 270 nm to 350 was observed. The responsivity curves diode modeled and compared experimental data.
We used Raman scattering and time-resolved photoluminescence spectroscopy to investigate the molecular-beam-epitaxy (MBE) growth parameters that optimize structural defects therefore internal radiative quantum efficiency of MBE-grown GaAs/AlGaAs double heterostructures (DH). The DH structures were grown at two different temperatures three As/Ga flux ratios determine conditions for an optimized structure with longest nonradiative minority carrier lifetime. measurements show improvement in...
Samples of HgCdSe alloys were grown via molecular beam epitaxy on thick ZnTe buffer layers Si substrates. Two Se sources used: an effusion cell loaded with 5N source material that produced a predominantly Se6 and cracker 6N could produce Se2 beam. The background electron concentration in as-grown samples was significantly reduced by switching to the source, going from 1017–1018 cm−3 3–5 × 1016 at 12 K. remained low even when cracking zone temperature lowered beam, which strongly suggests...