A5080020074- Semiconductor materials and devices
- Semiconductor Quantum Structures and Devices
- Advancements in Semiconductor Devices and Circuit Design
- GaN-based semiconductor devices and materials
- Advanced Semiconductor Detectors and Materials
- Semiconductor Lasers and Optical Devices
- Photonic and Optical Devices
- Semiconductor materials and interfaces
- Ga2O3 and related materials
- Radio Frequency Integrated Circuit Design
- Metal and Thin Film Mechanics
- Particle Detector Development and Performance
- Silicon Carbide Semiconductor Technologies
- Radiation Detection and Scintillator Technologies
- Radiation Effects in Electronics
- Dark Matter and Cosmic Phenomena
- Electron and X-Ray Spectroscopy Techniques
- Silicon and Solar Cell Technologies
- Microwave Engineering and Waveguides
- Quantum and electron transport phenomena
- Analog and Mixed-Signal Circuit Design
- Electromagnetic Simulation and Numerical Methods
- ZnO doping and properties
- Photocathodes and Microchannel Plates
- Nanowire Synthesis and Applications
University of Sheffield
2007-2020
University of Cambridge
2017
University of Manchester
2017
Engineering and Physical Sciences Research Council
2002-2003
Bell (Canada)
1989
University of Illinois Urbana-Champaign
1985
General Electric (United Kingdom)
1980
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...
A novel guarded surface leakage test structure is used to isolate the and bulk contributions gate current in AlGaN/GaN HFETs. Passivation with various recipes of SiN/sub x/ always resulted commonly observed increase leakage, which was found be dominated by through AlGaN. However, high temperature deposited gave a 1-2 orders reduction whereas low deposition an increase. Gate lag measurements were correlate closely component, giving direct evidence that key device problem slump associated flow...
The electron and hole multiplication coefficients, M/sub e/ h/, respectively, have been measured in thin GaAs homojunction PIN NIP diodes from conventional ionization analysis the effective /spl alpha/ beta/, determined. nominal intrinsic region thickness w of these structures ranges 1.0 mu/m down to 25 nm. In thicker structures, bulk-like behavior is observed; however, thinner significant differences are found. As i-regions become electric fields increase, e//M/sub h/ ratio seen approach...
Analytical expressions have been derived for the collector current, optical gain, and quantum efficiency a heterojunction, bi-polar phototransistor (HPT). These can be utilized to optimize current gain HPT design. The presence of avalanche multiplication in base-collector junction has taken into account shown significant factor determining an InGaAs/InP phototransistor. Experimental results versus collector-emitter voltage only explained terms Of multiplication.
AlGaN/GaN high electron mobility transistors are demonstrated with a very dc responsivity ( ~ 4.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> A/W at 5×10 xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> W) to UV light. The gain mechanisms in the device shown be due photo voltage effect both AlGaN barrier layer and GaN buffer layer. In case of absorption layer, trapped surface electrons, which characteristic unpassivated...
Both current-voltage and photoemission measurements of the conduction-band discontinuity same InGaP/GaAs p-n heterojunction have been carried out. Interpretation results using thermionic emission theory applied to a bipolar transistor resulted in offset value 0.21 eV case compositionally abrupt junction. This figure has confirmed by performing independent on
Dispersion in capacitance and conductance measurements AlGaN/GaN high-electron mobility transistors is typically interpreted as resulting from interface states. Measurements on varying gate-length devices a model of an interface-trap-free device are used to demonstrate that the distributed-resistance-induced dispersion significant for 1-MHz if gate length exceeds ~10 μm. Hence, state density using technique need use shorter order avoid this artefact.
We report the modification and control of threshold voltage in enhancement depletion mode AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors through use in-situ fluorine doping atomic layer deposition Al2O3. Uniform distribution F ions throughout oxide thickness are achievable, with a level up to 5.5 × 1019 cm−3 as quantified by secondary ion mass spectrometry. This reduces capacitive hysteretic effects when exploited GaN metal-oxide-semiconductor capacitors....
The effect of the growth temperature on properties InAlAs/AlGaAs quantum dots grown GaAs(100) substrates is investigated. optical efficiency and structural uniformity are improved by increasing from 530 to 560 °C. improvements quantum-dot characteristics could be explained suppressing incorporation oxygen formation group-III vacancies. Furthermore, edge-emitting laser diodes with six layers at °C have been fabricated. Lasing occurs via ground state 725 nm, a room-temperature threshold...
This paper describes a new comprehensive analytical charge-control model, which includes all the significant delays associated with heterojunction bipolar phototransistors (HPTs). A minimum number of approximations and assumptions have been made throughout its development. The model is accurate predictive provides an excellent insight into operation HPT since equations developed are based on fundamental charge control device operation. Realistic switching results up to 40 Gb/s, applicable...
All-GaN-integrated cascode heterojunction field effect transistors were designed and fabricated for power switching applications. A threshold voltage of +2 V was achieved using a fluorine treatment metal-insulator-semiconductor gate structure on the enhancement mode part. The device exhibited an output current 300 mA/mm by matching drivability both depletion parts. optimization shifting section to more negative value with addition dielectric layer under gate. performance compared equivalent...
Double heterostructure bipolar transistors have been fabricated on InP/InGaAs MBE material. Current gains of up to 80 observed in the emitter-up configuration. The devices were using two diffusion techniques and selective etching contact base.
Envelope tracking (ET) is a promising power amplifier (PA) architecture for current and future communications systems, which uses dynamic modulation of the supply voltage to provide high efficiency potentially very wide bandwidth over large range output power. However, nature can lead problematic variation in transistor gain, particularly GaN HEMTs. This paper describes analyzes this behavior detrimental effect it have on ET PAs. Contributing factors origins gain are described detail along...
Abstract AlGaN/GaN high electron mobility transistors with a range of dual metal gate (DMG) lengths have been fabricated and studied. An improvement in transconductance up to 9% has measured the DMG devices comparison conventional single devices. This is attributed distribution electric field under region as result two metals. The drain induced barrier lowering also suppressed using sub- µ m devices, decrease around 50% due potential shielding effect two-dimensional gas channel.
The electron multiplication factors in GaInP/GaAs single heterojunction bipolar transistors (HBT's) have been measured as a function of base-collector bias for range GaAs collector doping densities. In the lowest doped (5/spl times/10/sup 14/ cm/sup -3/) thick is determined by local electric field. As increases, found to be significantly reduced at low values from that predicted field profile. However, good agreement always high multiplication, close breakdown. This reduction fields...
The current transport mechanisms in double-heterojunction bipolar transistors, including the effects of conduction-band discontinuities spikes, is analyzed. Two approaches, one based on back-and-forth motion electrons base between confining spikes and other solution continuity equation base, are shown to be equivalent. simplified derivation Ebers-Moll-like terminal expressions ensures that physical have not been obscured. general model used match shape device DC characteristics successfully...
Double-heterojunction bipolar transistor structures in InP/GaInAs have been grown by low-pressure metal organic chemical vapour deposition. Good control of the Zn dopant GaInAs base layer was achieved, and devices with current gains up to 300 at densities 1.4kA/cm2 demonstrated.
A novel V-groove vertical heterostructure field effect transistor structure is proposed using semi-polar (11-22) GaN. crystallographic potassium hydroxide self-limiting wet etching technique was developed to enable a damage-free process. An AlGaN/GaN HFET successfully regrown by molecular beam epitaxy on the surface. smooth interface achieved which an essential requirement for formation of high mobility channel.
A study of the effect zinc diffusion into beryllium- and silicon-doped GaAs/Ga0.7Al0.3As structures has been carried out. The beryllium dopant was found to diffuse very rapidly as a result presence diffusing zinc, while silicon remained unaffected. mechanism is proposed whereby competition for gallium sites causes move interstitially wherever present.