A5103107103- GaN-based semiconductor devices and materials
- Ga2O3 and related materials
- Silicon Carbide Semiconductor Technologies
- ZnO doping and properties
- Semiconductor materials and devices
- Optical properties and cooling technologies in crystalline materials
- Plasma Diagnostics and Applications
- Thermal properties of materials
- Advanced Thermoelectric Materials and Devices
- Advanced DC-DC Converters
- Advanced Sensor and Energy Harvesting Materials
- Perovskite Materials and Applications
- Solid-state spectroscopy and crystallography
- Advancements in Semiconductor Devices and Circuit Design
- Electromagnetic Compatibility and Noise Suppression
- High voltage insulation and dielectric phenomena
- Electrohydrodynamics and Fluid Dynamics
- Semiconductor Quantum Structures and Devices
- Radiation Effects in Electronics
- Advanced Thermodynamics and Statistical Mechanics
- Optical Coatings and Gratings
- Thermal Radiation and Cooling Technologies
- Phase-change materials and chalcogenides
- Gyrotron and Vacuum Electronics Research
- Graphene research and applications
Virginia Tech
2005-2024
Avalanche and surge robustness involve fundamental carrier dynamics under high electric field current density. They are also prerequisites of any power device to survive common overvoltage overcurrent stresses in electronics applications such as vehicles, electricity grids, renewable energy processing. Despite tremendous efforts develop the next-generation devices using emerging ultra-wide bandgap semiconductors, lack effective bipolar doping has been a daunting obstacle for achieving...
Abstract Gallium nitride (GaN) is becoming a mainstream semiconductor for power and radio-frequency (RF) applications. While commercial GaN devices are increasingly being adopted in data centers, electric vehicles, consumer electronics, telecom defense applications, their performance still far from the intrinsic limit. In last few years, fin field-effect transistor (FinFET) trigate architectures have been leveraged to develop new generation of RF devices, which continuously advanced...
This work demonstrates five-channel AlGaN/ GaN Schottky barrier diodes (SBDs) fabricated on a 4-inch wafer with sheet resistance of 115 Ω/sq. A novel edge termination based regrown p-GaN is proposed to manage the electric field crowding in contact region. new self-aligned Ohmic process developed form sidewall all five channels single lithography step. The lateral SBDs breakdown voltage (BV) 1.65, 2.55, and 3.35 kV show Baliga's figure merit 3.1, 3.5, 3.6 GW/cm <sup...
This work demonstrates multi-channel AlGaN/GaN Schottky barrier diodes (SBDs) with a breakdown voltage (BV) over 10 kV, the highest BV reported in GaN devices to date. The epitaxial structure consists of p-GaN cap layer and five channels continuously grown on low-cost 4-inch sapphire substrate. A novel device design is proposed for electric field management, i.e., reduced surface (RESURF) structure, which balances net charges at reverse biases. SBD 98- μm anode-to-cathode length ( L <sub...
Edge termination is the enabling building block of power devices to exploit high breakdown field wide bandgap (WBG) and ultra-wide (UWBG) semiconductors. This work presents a heterogeneous junction extension (JTE) based on p-type nickel oxide (NiO) for gallium (Ga2O3) devices. Distinct from prior JTEs usually made by implantation or etch, this NiO JTE deposited surface Ga2O3 magnetron sputtering. The consists multiple layers with various lengths allow graded decrease in effective charge...
GaN high electron mobility transistors (HEMTs) have limited avalanche capability and usually fail catastrophically in voltage overshoot up to their dynamic breakdown (BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dyn</sub> ). This article presents the first comparative study of parametric shift recovery three mainstream HEMTs repetitive overvoltage switching near BV . In each cycle, a 90% was applied during turn- <sc...
In this Letter, we show the phonon dispersion of ${({\mathrm{CH}}_{3}{\mathrm{NH}}_{3})}_{3}{\mathrm{Bi}}_{2}{\mathrm{I}}_{9}$ single crystals at 300 K measured by inelastic x-ray scattering. The frequencies acoustic phonons are among lowest crystals. Nanoindentation measurements verified that these very compliant and considerably soft. frequency overlap between optical results in strong acoustic-optical All features lead to an ultralow thermal conductivity. fundamental knowledge obtained...
We report the first experimental demonstration of a vertical superjunction device in GaN. P-type nickel oxide (NiO) is sputtered conformally $6 \mu \mathrm{m}$ deep n-GaN trenches. Sputter recipe tuned to enable $10 ^{17}$ cm $^{-3}$ level acceptor concentration NiO, easing its charge balance with $9 \times 10 ^{16}$ doped n-GaN. Vertical GaN p-n diodes (SJ-PNDs) are fabricated on both native and low-cost sapphire substrates. SJ-PNDs show breakdown voltage $( BV)$ 1100 V, being at least 900...
Thermal switches are of great importance to thermal management in a wide variety applications. However, traditional suffer from being large and having slow transition rates. To overcome these limitations, we took advantage abrupt second-order phase transitions thermoresponsive polymer aqueous solutions enable fast switching. While polymers have been widely studied for biomedical applications, their switching capability has not studied. In this work, used poly(N-isopropylacrylamide) (PNIPAM)...
This work presents a new device concept, the Multi-Channel Monolithic-Cascode high-electron-mobility transistor (MC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -HEMT), which monolithically integrates low-voltage, enhancement-mode (E-mode) HEMT based on single 2DEG channel and high-voltage, depletion-mode (D-mode) stacked multi-channel. can exploit low sheet resistance of multi-channel, realize an E-mode gate control, completely...
The thermal conductivity of crystalline polymers is higher than their amorphous counterparts yet still spans three orders magnitude. In this study, by quantifying intrinsic properties including bond energy, backbone rotation, in-plane ratio, and atomic mass, we develop a theoretical model to predict based on given unit cell. This can be readily applied estimate without large-scale simulations or experimental measurements. could advance fundamental understanding transport in guide the...
This work presents a tri-gate GaN junction high-electron-mobility transistor (JHEMT) concept in which the p–n wraps around AlGaN/GaN fins gate region. JHEMT differs from all existing FinFETs and HEMTs, as they employ Schottky or metal-insulator-semiconductor (MIS) stack. A is fabricated using p-type NiO with metal forming an Ohmic contact to NiO. The device shows minimal hysteresis subthreshold slope of 63 ± 2 mV/decade on-off current ratio 108. Compared MISHEMTs on same wafer, JHEMTs...
This work demonstrates multi-kilovolt AlGaN/GaN Schottky barrier diodes (SBDs) on a 4-inch, five-channel, low-cost GaN-on-sapphire wafer. Our device highlights new 3-D anode architecture, in which the p-n junction wraps around multi-2DEG-channel fins. junction-fin structure differs from all existing tri-anode and tri-gate structures, employ or metal-insulator-semiconductor (MIS) stack at fin sidewalls. is realized with regrown p-GaN top of p-type NiO <inf...
Today and in the future, a huge market arises for mobile power . Efficient performance, functionality, small profile low cost are most desired features management integrated circuits. Compared with discrete-switching dc-dc converter, monolithic integration offers many benefits new design challenges. In this paper, monolithically high-efficiency boost converter nickel metal hydride or alkaline battery-powered applications is designed based on low-voltage CMOS process. Several novel concepts...
Hybrid organic–inorganic perovskites were reported to have ultralow thermal conductivity in recent studies. In this Letter, we report the first experimental phonon dispersion and lifetimes of tetragonal CH3NH3PbI3 single crystals at both 200 300 K by high-energy resolution inelastic X-ray scattering, which enables a thorough understanding underlying mechanisms for conductivity. Notably, observed unusual significant dips along [100] [110] directions temperatures. The can be attributed small...
We present the physics and performance space of tri-gate GaN junction high electron mobility transistor (Tri-JHEMT), a new device proposed recently. In Tri-JHEMTs, p-n junctions wrap around two-dimensional-electron-gas (2DEG) fins in gate region. Our fabricated Tri-JHEMT demonstrates, for first time, kilovolt blocking capability at 150 °C all transistors (HEMTs). Three-dimensional TCAD simulations were then calibrated with experimental devices used to study p-GaN-based Tri-JHEMTs...
Many emerging GaN electronic and optoelectronic devices comprise p-GaN layers buried below n-GaN or AlGaN. The activation of these usually relies on the lateral hydrogen diffusion through etched mesa sidewalls, which is known to induce nonuniform acceptor distributions. However, profile, electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> -field) blocking...
Recent progress in p-GaN trench-filling epitaxy has shown promise for the demonstration of GaN superjunction (SJ) devices. However, presence n-type interface charges at regrowth interfaces been widely observed. These pose great challenges to design and performance evaluation SJ This work presents an analytical model devices with first time. In our model, two approaches are proposed compensate charges, by modulation doping or geometry. Based on study is conducted transistors, revealing...
This paper presents the evaluation of a 650-V, 100- A, 22-m$\Omega$ rated $\text{D}^{3}$GaN (Direct Drive Depletion-mode) power switch (V22TC6581A) from VisIC Technologies, which is designed for electric vehicles (EV) powertrain inverter applications. The static and dynamic performance as well surge-energy short-circuit robustness were evaluated in top-cooled surface-mount device package. Multiple customized test boards employed to evaluate switching loss, on-resistance, gate charge...
The lack of reports on the high-temperature performance tri-gate GaN power HEMTs has raised serious concern their competitiveness. This work demonstrates first normally-off HEMT that can block kilovolts at 150 °C and zero gate bias. key enabling device design is a new type tri-gate, junction which comprises p-n wrapping around AlGaN/GaN fins in region. At °C, (Tri-JHEMT) retains strong control stable threshold voltage, while traditional metal-insulator-semiconductor (MIS) fabricated same...
The overvoltage and surge energy robustness of GaN power high-electron-mobility transistors (HEMTs) is a key gap recently identified by the JEDEC JC-70.1 committee. This work presents first study on parametric shift recovery an industrial depletion-mode metal-insulator-semiconductor HEMT (MIS-HEMT) in repetitive switching close to its dynamic breakdown voltage. In each cycle, voltage overshoot up 90% was applied during device turn-OFF process. As prolongs, showed shifts threshold voltage,...
A major challenge in the design and fabrication of power devices from ultra-wide bandgap (UWBG) materials is lack a native shallow acceptor dopant for most that class. P-type regions UWBG may alternatively be formed by deposition p-type wide such as nickel oxide (NiO) to form heterojunctions. This work examines effectiveness modulation concentration $\left(N_{\mathrm{A}}\right)$ magnetron sputtered NiO via control O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML"...