Dennis E. Walker
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View article: Two-Stage Hybrid Optimization of Topology and Infill Density in Polymer Extrusion Additive Manufacturing for Lightweight High-Integrity Structures
Two-Stage Hybrid Optimization of Topology and Infill Density in Polymer Extrusion Additive Manufacturing for Lightweight High-Integrity Structures Open
Material Extrusion (MEX) additive manufacturing offers a versatile platform for producing lightweight, structurally optimized components. This study investigates the simultaneous optimization of topology and infill density using three poly…
View article: Enhanced anti-crossing in resonant reflection via structured waveguide gratings
Enhanced anti-crossing in resonant reflection via structured waveguide gratings Open
Gratings with structured periods allow for a controlled ratio between the strength of optical coupling in different diffraction orders. A structured waveguide grating may produce relatively weak coupling in the first diffraction order lead…
View article: A scattering matrix approach to the effective mass dependence of tunneling current through heterojunctions
A scattering matrix approach to the effective mass dependence of tunneling current through heterojunctions Open
A scattering matrix technique is used to calculate the longitudinal and transverse energy dependence of the transmission probability through various heterostructures using both the BenDaniel–Duke (BD) and the lesser known Zhu–Kroemer (ZK) …
View article: Field emission characteristics of AlGaN/GaN nanoscale lateral vacuum diodes
Field emission characteristics of AlGaN/GaN nanoscale lateral vacuum diodes Open
We report the design, fabrication, and measurement of the field emission (FE) characteristics of AlGaN/GaN nanoscale lateral vacuum diodes with triangular cathodes and cathode to anode spacings from 50 to 600 nm. The FE characteristics of …
View article: An ASM-HEMT for Large-Signal Modeling of GaN HEMTs in High-Temperature Applications
An ASM-HEMT for Large-Signal Modeling of GaN HEMTs in High-Temperature Applications Open
This paper reports a temperature-dependent ASM-HEMT for modeling GaN HEMTs at elevated temperatures. Modifications to the standard ASM-HEMT were developed to accurately capture the DC and RF measurements collected at varying chuck temperat…
View article: Scaled T-Gate <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> MESFETs With 2.45 kV Breakdown and High Switching Figure of Merit
Scaled T-Gate <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> MESFETs With 2.45 kV Breakdown and High Switching Figure of Merit Open
We demonstrate a passivated MESFET fabricated on (010) Si-doped -Ga 2 O 3 with breakdown over 2.4 kV without field plates, high Power Figure of Merit (PFOM), and high estimated Huang's Material Figure of Merit (HMFOM), owing to low gate c…
View article: RF Power Performance of Sc(Al,Ga)N/GaN HEMTs at Ka-Band
RF Power Performance of Sc(Al,Ga)N/GaN HEMTs at Ka-Band Open
We report the RF power results of Sc(Al,Ga)N/GaN high electron mobility transistors (HEMTs). We show dc, small-signal RF and load-pull performance at 30 GHz with two barrier alloys-a ternary of ScAlN and a quaternary of ScAlGaN. The active…
View article: Pulsed Power Performance of <i>β</i>-Ga₂O₃ MOSFETs at L-Band
Pulsed Power Performance of <i>β</i>-Ga₂O₃ MOSFETs at L-Band Open
DC, small, and large signal results are shown under continuous wave and pulsed conditions for a β-Ga 2 O 3 metal-oxide-semiconductor field-effect transistor operating at 1 and 2 GHz. The device has a maximum transducer gain, maximum output…
View article: Lateral β-Ga<sub>2</sub>O<sub>3</sub> field effect transistors
Lateral β-Ga<sub>2</sub>O<sub>3</sub> field effect transistors Open
Beta phase Gallium Oxide (BGO) is an emerging ultra-wide bandgap semiconductor with disruptive potential for ultra-low power loss, high-efficiency power applications. The critical field strength is the key enabling material parameter of BG…
View article: ScAlN/GaN High-Electron-Mobility Transistors With 2.4-A/mm Current Density and 0.67-S/mm Transconductance
ScAlN/GaN High-Electron-Mobility Transistors With 2.4-A/mm Current Density and 0.67-S/mm Transconductance Open
We report the dc and RF performance of ScAlN/GaN high-electron-mobility transistors (HEMTs). The ScAlN/GaN material was epitaxially grown onto a GaN template on a 4-in 4H-SiC substrate by molecular beam epitaxy. The sheet resistance was me…
View article: Experimental Observation of Strong Coupling Between an Epsilon-Near-Zero Mode in a Deep Subwavelength Nanofilm and a Gap Plasmon Mode
Experimental Observation of Strong Coupling Between an Epsilon-Near-Zero Mode in a Deep Subwavelength Nanofilm and a Gap Plasmon Mode Open
Strong coupling is a phenomenon which occurs when the interaction between two resonance systems is so strong that the oscillatory energy exchange between them exceeds all dissipative loss channels. Each resonance can then no longer be desc…
View article: Flexible Gallium Nitride: Flexible Gallium Nitride for High‐Performance, Strainable Radio‐Frequency Devices (Adv. Mater. 47/2017)
Flexible Gallium Nitride: Flexible Gallium Nitride for High‐Performance, Strainable Radio‐Frequency Devices (Adv. Mater. 47/2017) Open
In article number 1701838, Nicholas R. Glavin and co-workers describe the use of a series of flexible gallium nitride radio-frequency devices for power amplification of wireless signals at high frequencies for future wearable and conformal…
View article: Enhancement-mode Ga2O3 wrap-gate fin field-effect transistors on native (100) <i>β</i>-Ga2O3 substrate with high breakdown voltage
Enhancement-mode Ga2O3 wrap-gate fin field-effect transistors on native (100) <i>β</i>-Ga2O3 substrate with high breakdown voltage Open
Sn-doped gallium oxide (Ga2O3) wrap-gate fin-array field-effect transistors (finFETs) were formed by top-down BCl3 plasma etching on a native semi-insulating Mg-doped (100) β-Ga2O3 substrate. The fin channels have a triangular cross-sectio…
View article: Label-free nanoscopy with contact microlenses: Super-resolution mechanisms and limitations
Label-free nanoscopy with contact microlenses: Super-resolution mechanisms and limitations Open
Despite all the success with developing super-resolution imaging techniques, the Abbe limit poses a severe fundamental restriction on the resolution of far-field imaging systems based on diffraction of light. Imaging with contact microlens…
View article: Label-Free Nanoscopy with Contact Microlenses: Super-Resolution\n Mechanisms and Limitations
Label-Free Nanoscopy with Contact Microlenses: Super-Resolution\n Mechanisms and Limitations Open
Despite all the success with developing super-resolution imaging techniques,\nthe Abbe limit poses a severe fundamental restriction on the resolution of\nfar-field imaging systems based on diffraction of light. Imaging with contact\nmicrol…
View article: Probing phonon and electrical anisotropy in black phosphorus for device alignment
Probing phonon and electrical anisotropy in black phosphorus for device alignment Open
Black phosphorus has emerged as a promising two-dimensional semiconductor, which has a unique structure that is anisotropic in-plane. This structural anisotropy translates to some very interesting orientation dependent properties. In this …
View article: Fundamental limits of super-resolution microscopy by dielectric microspheres and microfibers
Fundamental limits of super-resolution microscopy by dielectric microspheres and microfibers Open
In recent years, optical super-resolution by microspheres and microfibers emerged as a new paradigm in nanoscale label-free and fluorescence imaging. However, the mechanisms of such imaging are still not completely understood and the resol…
View article: Overcoming the diffraction limit of imaging nanoplasmonic arrays by microspheres and microfibers
Overcoming the diffraction limit of imaging nanoplasmonic arrays by microspheres and microfibers Open
Super-resolution microscopy by microspheres emerged as a simple and broadband imaging technique; however, the mechanisms of imaging are debated in the literature. Furthermore, the resolution values were estimated based on semi-quantitative…
View article: Implementation of High-Power-Density <inline-formula> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula>-Band AlGaN/GaN High Electron Mobility Transistors in a Millimeter-Wave Monolithic Microwave Integrated Circuit Process
Implementation of High-Power-Density -Band AlGaN/GaN High Electron Mobility Transistors in a Millimeter-Wave Monolithic Microwave Integrated Circuit Process Open
A GaN high electron mobility transistor monolithic microwave integrated circuit (MMIC) designer typically has to choose a device design either for high-gain millimeter-wave operation with a short gate length, or for high-power-density -ba…
View article: Movable thin films with embedded high-index microspheres for super-resolution microscopy
Movable thin films with embedded high-index microspheres for super-resolution microscopy Open
Microsphere-assisted imaging emerged as a surprisingly simple way of achieving optical super-resolution imaging. In this work, we use movable PDMS thin films with embedded high-index barium titanate glass microspheres a sample scanning cap…
View article: Super‐resolution microscopy by movable thin‐films with embedded microspheres: Resolution analysis
Super‐resolution microscopy by movable thin‐films with embedded microspheres: Resolution analysis Open
Microsphere‐assisted imaging has emerged as an extraordinary simple technique of obtaining optical super‐resolution. This work addresses two central problems in developing this technology: i) methodology of the resolution measurements and …