A5081176603- GaN-based semiconductor devices and materials
- Semiconductor materials and devices
- Silicon Carbide Semiconductor Technologies
- Semiconductor Quantum Structures and Devices
- Ga2O3 and related materials
- Thermal properties of materials
- ZnO doping and properties
- Metal and Thin Film Mechanics
- Advancements in Semiconductor Devices and Circuit Design
- Acoustic Wave Resonator Technologies
- Diamond and Carbon-based Materials Research
- Boron and Carbon Nanomaterials Research
- Radio Frequency Integrated Circuit Design
- Nanowire Synthesis and Applications
- Electronic and Structural Properties of Oxides
- Thin-Film Transistor Technologies
- Advanced Photocatalysis Techniques
- Semiconductor Lasers and Optical Devices
- 2D Materials and Applications
- Semiconductor materials and interfaces
- Thermal Radiation and Cooling Technologies
- Advanced ceramic materials synthesis
- Integrated Circuits and Semiconductor Failure Analysis
- Superconducting and THz Device Technology
- Photonic and Optical Devices
University of Bristol
2016-2025
Bristol Robotics Laboratory
2001-2025
At Bristol
2023-2024
Cardiff University
2023
University of Oxford
2022
Northrop Grumman (United States)
2022
United States Air Force Research Laboratory
2022
Argonne National Laboratory
2022
University of Notre Dame
2022
University of Sheffield
2021
Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in industry silicon-based and currently faced with diminishing returns of performance versus cost investment. At material level, its high electric field strength electron mobility have already shown for frequency communications photonic applications. Advances on commercially viable large area substrates are now at the point where power conversion applications GaN cusp...
The bulk trap-induced component of current collapse (CC) in GaN/AlGaN heterojunction field-effect transistors is studied drift diffusion simulations, distinguishing between acceptor traps situated the top and bottom half bandgap, with Fe C used as specific examples. It shown that doping results an inherent but relatively minor contribution to dispersion under pulse conditions. This simulation reasonable quantitative agreement double experiments. Simulations using deep-level intrinsic growth...
GaN-on-Si power switching transistors that use carbon-doped epitaxy are highly vulnerable to dynamic R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> dispersion, leading reduced efficiency. In this paper, we identify the causes of dispersion using substrate bias ramps isolate leakage paths and trapping locations in simulation their impact on device characteristics. It is shown can occur both vertically laterally, suggest associated not...
Abstract Hexagonal boron nitride (h-BN) has been predicted to exhibit an in-plane thermal conductivity as high ~ 550 W m −1 K at room temperature, making it a promising management material. However, current experimental results (220–420 ) have well below the prediction. Here, we report on modulation of h-BN by controlling B isotope concentration. For monoisotopic 10 h-BN, 585 is measured 80% higher than that with disordered concentration (52%:48% mixture and 11 B). The temperature-dependent...
In this work, the possibility of using different generations <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> -Ga <sub xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as an ultra-wide-bandgap power semiconductor device for high converter applications is explored. The competitiveness converters in still not well...
Abstract The use of micro‐Raman spectroscopy to monitor non‐invasively GaN, AlGaN and AlN material parameters for process growth monitoring/control is demonstrated. Concepts determine the crystalline quality, stress, free carrier concentration, aluminium composition temperature from Raman modes are reviewed. monitoring processing illustrated on selected examples: high‐temperature ion‐implanted non‐implanted GaN layers, AlGaN/GaN heterostructure field‐effect transistors in situ at elevated...
We report on the noninvasive measurement of temperature, i.e., self-heating effects, in active AlGaN/GaN HFETs grown sapphire and SiC substrates. Micro-Raman spectroscopy was used to produce temperature maps with /spl ap/1 μm spatial resolution a accuracy better than 10/spl deg/C. Significant rises up 180/spl deg/C were measured device gate-drain opening. Results from three-dimensional (3-D) heat dissipation model are reasonably good agreement experimental data. Comparison devices fabricated...
The influence of a thermal boundary resistance (TBR) on temperature distribution in ungated AlGaN/GaN field-effect devices was investigated using 3-D micro-Raman thermography. operating SiC, sapphire, and Si substrates used to determine values for the TBR by comparing experimental results finite-difference simulations. While measured about 3.3 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> W...
Self-heating in AlGaN/GaN device structures was probed using integrated micro-Raman/Infrared (IR) thermography. IR imaging provided large-area-overview temperature maps of powered devices. Micro-Raman spectroscopy used to obtain high-spatial-resolution profiles over the active area Depth scans were performed heat-sinking SiC substrate. Limitations and spatial resolution, relative advantages both techniques are discussed. Results compared three-dimensional finite-difference simulations
A composition-temperature phase diagram of the system (1−x)(K0.5Na0.5)NbO3–xLiNbO3 is presented for 0⩽x⩽0.1. Using dielectric and piezoelectric resonance measurements, Raman spectroscopy, ceramic samples containing 2%–10% LiNbO3 were studied over a temperature range 7–770K showing complex sequence transitions. Analysis different Raman, piezoelectric, data shows distinct transitions from cubic to tetragonal orthorhombic rhombohedral x=0.02–0.05. The symmetries phases assigned using analogy...
A thermal boundary resistance (TBR) is associated with the presence of an AlN nucleation layer (NL) in AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on SiC substrates, raising device temperature beyond what expected from simple conductivities main layers. TBR was found to differ by up a factor four between different suppliers, all using standard metal-organic chemical vapor deposition (MOCVD) growth techniques, related detailed NL microstructure. Optimizing crystalline structure...
Integration of chemical vapor deposited polycrystalline diamond offers promising thermal performance for GaN-based high power radio frequency amplifiers. One limiting factor is the barrier at GaN to interface, often referred as effective boundary resistance (TBReff). Using a combination transient thermoreflectance measurement, finite element modeling and microstructural analysis, TBReff GaN-on-diamond wafers shown be dominated by SiNx interlayer growth seeding, with additional impacts from...
A new methodology is developed to determine spatial location and properties of traps generated by electrical stressing AlGaN/GaN high-electron mobility transistors, based on integrated optical analysis. Mild off-state stress increases irreversibly the number located in near-surface AlGaN region at gate edge. deep level with 0.45-eV activation energy fresh devices changes its nature interacting defect after stress, accompanied an change. These results are consistent trap generation edge...
The development of GaN-on-diamond devices holds much promise for the creation high-power density electronics. Inherent to growth these devices, a dielectric layer is placed between GaN and diamond, which can contribute significantly overall thermal resistance structure. In this work, we explore role different interfaces in contributing interface GaN/diamond layers, specifically using 5 nm layers AlN, SiN, or no interlayer at all. Using time-domain thermoreflectance along with electron energy...
GaN-on-diamond device cooling can be enhanced by reducing the effective thermal boundary resistance (TBReff) of GaN/diamond interface. The properties this interface and polycrystalline diamond grown onto GaN using SiN AlN barrier layers as well without any layer under different growth conditions are investigated systematically compared for first time. TBReff values correlated with transmission electron microscopy analysis, showing that lowest reported (∼6.5 m2 K/GW) is obtained ultrathin a...
Polycrystalline diamond (PCD) was grown onto high-k dielectric passivated AlGaN/GaN-on-Si high electron mobility transistor (HEMT) structures, with film thicknesses ranging from 155 to 1000 nm. Transient thermoreflectance results were combined device thermal simulations investigate the heat spreading benefit of layer. The observed conductivity (κDia) PCD films is one-to-two orders magnitude lower than that bulk and exhibits a strong layer thickness dependence, which attributed grain size...
Dynamic transconductance dispersion measurements coupled with device physics simulations were used to study the deep level acceptor center in iron-doped AlGaN/GaN high electron mobility transistors (HEMT). From extracted frequency dependent trap-conductance, an energy 0.7 eV below conduction band and a capture cross section of 10−13 cm2 obtained. The approach presented this work avoids non-equilibrium electrical or optical techniques that have been date extracts relevant trap characteristics...
Dynamic on -resistance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(R_{\rm ON})$</tex></formula> in heavily carbon-doped AlGaN/GaN high electron mobility transistors is shown to be associated with the semi-insulating buffer region. Using transient substrate bias, differences Notation="TeX">$R_{\rm ON}$</tex></formula> dispersion between fabricated nominally identical epilayer structures were...
A strong positive correlation between dynamic Ron and the ionization of buffer traps by injection electrons from Si substrate is presented. By exploring different Carbon doping profiles in epi layers, leakage substantially reduced, which turns results lower Ron. The structure are characterized electrical techniques such as drain current transient, on-the-fly trapping ramped back-gating experiments.
Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in buffer layers carbon doped GaN power heterojunction field effect transistor. Carbon multiple AlGaN alloy these devices deliver an insulating strain relieved with high breakdown voltage capability. However, physical mechanism for its operation is still lacking. At lowest electric fields (&lt;10 MV/m), charge redistribution within C layer...
The implementation of 5G-and-beyond networks requires faster, high-performance, and power-efficient semiconductor devices, which are only possible with materials that can support higher frequencies. Gallium nitride (GaN) power amplifiers essential for technologies since they provide the desired combination high frequency power. These applications along terrestrial hub backhaul communications at output present severe heat removal challenges. cooling GaN devices diamond as spreader has gained...
Abstract Thick metamorphic buffers are considered indispensable for III‐V semiconductor heteroepitaxy on large lattice and thermal‐expansion mismatched silicon substrates. However, III‐nitride in conventional GaN‐on‐Si high electron mobility transistors (HEMT) impose a substantial thermal resistance, deteriorating device efficiency lifetime by throttling heat extraction. To circumvent this, systematic methodology the direct growth of GaN after AlN nucleation layer six‐inch substrates is...
The temperature distribution in multifinger high-power AlGaN/GaN heterostructure field-effect transistors grown on SiC substrates was studied. Micro-Raman spectroscopy used to measure channel with 1 μm spatial resolution, not possible using infrared techniques. Thermal resistance values were determined for four different device layouts varying number of fingers, finger width, and spacing. experimental thermal fair agreement that predicted by three-dimensional finite difference heat...