M.J. Kelly

M.J. Kelly
University of Cambridge | Cam

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263
Publications
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3,475
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Publications

Publications (263)
Article
Full-text available
Metamaterial photonic integrated circuits with arrays of hybrid graphene–superconductor coupled split-ring resonators (SRR) capable of modulating and slowing down terahertz (THz) light are introduced and proposed. The hybrid device’s optical responses, such as electromagnetic-induced transparency (EIT) and group delay, can be modulated in several w...
Preprint
Full-text available
Metamaterial photonic integrated circuits with arrays of hybrid graphene-superconductor coupled split-ring resonators (SRR) capable of modulating and slowing down terahertz (THz) light are introduced and proposed. The hybrid device optical responses, such as electromagnetic induced transparency (EIT) and group delay, can be modulated in several way...
Article
In the present work, we have systematically investigated the design of Asymmetric SPAcer-layer Tunnel (ASPAT) diodes using numerical modeling employing SILVACO Atlas software. After reproducing and validating physical models using experimental data obtained from fabricated ASPAT diodes, a developed SILVACO model was used to evaluate the effect of d...
Article
Full-text available
We present multiplexer methodology and hardware for nanoelectronic device characterization. This high-throughput and scalable approach to testing large arrays of nanodevices operates from room temperature to milli-Kelvin temperatures and is universally compatible with different materials and integration techniques. We demonstrate the applicability...
Preprint
Full-text available
Several theoretical studies have recently predicted that the Majorana phases could be realized as quantized plateaus in the magnetoconductance of the artificially engineered hybrid junctions based on two-dimensional electron gases (2DEG) under fully out-of-plane magnetic fields. The large transverse Rashba spin-orbit interaction in 2DEG together wi...
Conference Paper
This work reports on a novel temperature-insensitive zero-bias GaAs/AlAs Asymmetric Spacer Layer Tunnel diode (ASPAT) detector with a curvature coefficient is 18V-1. The detector was fabricated and experimentally measured in the frequency band (15 to 35) GHz at various input powers. The maximum measured sensitivity is 1300 V/W at 24GHz for a -27dBm...
Article
To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrier-free interface between two different materials is necessary. The S-Sm junction with high interface transparency will then facilitate the observation of the induced hard superconducting gap, which is the key requir...
Conference Paper
Full-text available
In this paper, the subharmonic energy gap structures (SGS) and induced superconductivity, due to multiple Andreev reflections, in indium gallium arsenide (In 0.75 Ga 0.25 As) two-dimensional electron gas (2DEG) are discussed at different temperatures and magnetic fields. Strong suppression of both SGS and induced gap are observed as a function of t...
Article
Full-text available
In this paper, the subharmonic energy gap structures (SGS) and induced superconductivity, due to multiple Andreev reflections, in indium gallium arsenide (In0.75Ga0.25As) two-dimensional electron gas (2DEG) are discussed at different temperatures and magnetic fields. Strong suppression of both SGS and induced gap are observed as a function of tempe...
Presentation
Due to their potential for ultra-high bandwidth, short-haul Gb/s wireless transmission, the millimeter and sub-millimeter regions of the electromagnetic spectrum have been extensively investigated. One of the most appealing candidates for realizing a room temperature, a compact and high output power source, which has the capability to effectively...
Article
In this paper, we experimentally demonstrate a hybrid superconducting-semiconducting (S-Sm) circuit consisting of eight planar and ballistic Nb-In0.75Ga0.25As-Nb Josephson junctions. E-beam lithography was used to fabricate the Josephson junctions on an InGaAs chip. In contrast to our previous studies on long junctions that were fabricated by photo...
Article
In this paper, we experimentally demonstrate a hybrid superconducting-semiconducting (S-Sm) circuit consisting of eight planar and ballistic Nb-In0.75Ga0.25As-Nb Josephson junctions. E-beam lithography was used to fabricate the Josephson junctions on an InGaAs chip. In contrast to our previous studies on long junctions that were fabricated by photo...
Article
We report on the experimental observation of the proximity induced superconductivity in an indium gallium arsenide (In0.75Ga0.25As) quantum well. The Josephson junction was fabricated by several photo-lithographic processes on an InGaAs heterojunction and Niobium (Nb) was used as superconducting electrodes. Owing to the Andreev reflections and Andr...
Article
Full-text available
This work presents an experimental study of InGaAs/AlAs resonant tunneling diodes designed to improve the diode characteristics using five different device structures. A promising high peak to valley current ratio of 5.2 was obtained for a very low current density device. As expected, the measured results show a significant increase in the current...
Article
Full-text available
A complete description of physical models for fabricated asymmetric spacer tunnel layer (ASPAT) diodes is reported in this paper. A novel In0.53Ga0.47As/AlAs design is presented and compared to the conventional GaAs/AlAs material system. For both material schemes, physical models were developed based on experimental measurements. Simulated dc chara...
Article
We report on the experimental observation of the proximity induced superconductivity in an indium gallium arsenide (In0.75Ga0.25As) quantum well. The Josephson junction was fabricated by several photo-lithographic processes on an InGaAs heterojunction and Niobium (Nb) was used as superconducting electrodes. Owing to the Andreev reflections and Andr...
Article
We introduce a class of low-loss subwavelength resonators and report the first demonstration of a high-temperature (Tc) superconducting Bi2Sr2CaCu2O8+d (BSCCO) terahertz (THz) metamaterial. The numerical simulations and analytical calculations are performed to study the electromagnetic response of the subwavelength BSCCO split-ring resonators (SRRs)...
Article
Full-text available
We introduce a class of low-loss subwavelength resonators and report on the first demonstration of a high-temperature ( $T_{c}$ ) superconducting ${\rm Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}}$ (BSCCO) terahertz (THz) metamaterial. The numerical simulations and analytical calculations are performed to study the electromagnetic response of the subwavelengt...
Article
A superconducting hard gap in hybrid superconductor–semiconductor devices has been found to be necessary to access topological superconductivity that hosts Majorana modes (non-Abelian excitation). This requires the formation of homogeneous and barrier-free interfaces between the superconductor and semiconductor. Here, a new platform is reported for...
Article
A superconducting hard gap in hybrid superconductor-semiconductor devices has been found to be necessary to access topological superconductivity that hosts Majorana modes (non-Abelian excitation). This requires the formation of homogeneous and barrier-free interfaces between the superconductor and semiconductor. Here, a new platform is reported for...
Conference Paper
The following topics are dealt with: Josephson effect; SQUIDs; high-temperature superconductors; nanowires; superconducting thin films; superconducting photodetectors; readout electronics; superconducting materials; critical current density (superconductivity); photon counting.
Article
Paul Callaghan will be remembered internationally for many seminal contributions to the foundations of magnetic resonance imaging as applied to the rheological analysis of a series of real world materials – paints, gels, polymer solutions – and at home in New Zealand as the leading physical scientist of his day, who became a familiar science commun...
Conference Paper
Full-text available
Submitted for the MAR17 Meeting of The American Physical Society, Coherent quantum transport in hybrid Nb-InGaAs-Nb Joseph-son junctions KAVEH DELFANAZARI, — Because of the recently reported detection of Majorana fermions states at the superconductor-semiconductor (S-Sm) interface in InAs nanowire devices, the study of hybrid structures has receive...
Chapter
Artefacts in widespread use in electronic and optoelectronic systems have been manufactured by low-cost, high-volume processes. This chapter reviews recent progress and lack of progress on manufacturability of several nanoscale systems using the criteria: tunnel devices, split-gate transistors/quantum point contacts, and other nanoscale systems. Fo...
Conference Paper
The uniformity of RF characteristics of GaAs/AlAs Asymmetric spacer layer tunnel diode (ASP AT) is presented for the first time in this report. The variations of S-parameter at zero bias across all devices at 5, 10, 15, and 20 GHz have been investigated, all of which are below 3%, making the ASPAT diodes further promising for manufacturing.
Article
We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs/AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization decreases rapidly as the length of the split gates increases. Howev...
Article
2016 American Physical Society. © 2016 American Physical Society.We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs/AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization de...
Article
There are lessons from recent history of technology introductions which should not be forgotten when considering alternative energy technologies for carbon dioxide emission reductions. The growth of the ecological footprint of a human population about to increase from 7B now to 9B in 2050 raises serious concerns about how to live both more efficie...
Article
For a science to become a technology, a certain level of control has to have been established over the way items are fabricated for manufacture and use. Here we first consider the challenge of making and using a LEGO® brick scaled down by a factor of 10n for n = 0–6 in each spatial dimension, i.e. from millimetres to nanometres. We consider both th...
Article
We present a method of forming and controlling large arrays of gate-defined quantum devices. The method uses an on-chip, multiplexed charge-locking system and helps to overcome the restraints imposed by the number of wires available in cryostat measurement systems. The device architecture that we describe here utilises a multiplexer-type scheme to...
Article
Full-text available
We utilize a multiplexing architecture to measure the conductance properties of an array of 256 split gates. We investigate the reproducibility of the pinch off and one-dimensional definition voltage as a function of spatial location on two different cooldowns, and after illuminating the device. The reproducibility of both these properties on the t...
Article
Full-text available
We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs/AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization decreases rapidly as the length of the split gates increases. Howev...
Article
We report on the final steps needed to achieve the level of control over the properties of single tunnel barriers of AlAs needed to allow the manufacture of high-volume low-cost microwave and millimeter-waves detectors. We achieve a 1% standard deviation of the current-voltage characteristics across 2-in wafers and average currents from different w...
Article
Conductance data from 256 multiplexed split gate devices, measured during a single cooldown to 1.4 K. These data support the paper entitled ‘Dependence of the 0.7 anomaly on the curvature of the potential barrier in quantum wires’ by L. W. Smith et al. It includes .csv files of the raw data prior to any data analysis, and data necessary to produce...
Article
Full-text available
Ninety eight one-dimensional channels defined using split gates fabricated on a GaAs/AlGaAs heterostructure are measured during one cooldown at 1.4 K. The devices are arranged in an array on a single chip, and individually addressed using a multiplexing technique. The anomalous conductance feature known as the "0.7 structure" is studied using stati...
Article
A multiplexer technique is used to individually measure an array of 256 split gates on a single GaAs/AlGaAs heterostructure. This results in the generation of large volumes of data, which requires the development of automated data analysis routines. An algorithm is developed to find the spacing between discrete energy levels, which form due to tran...
Article
This paper presents a method to tune an arbitrary number of split-gate transistors in series to their threshold voltage, prior to initiating any particular experiment. The model accounts for device variations and considers coupled/uncoupled electrical gates and ballistic/ohmic addition of resistances. Experimental verification of this 'zeroing meth...
Article
Full-text available
We present a method of forming and controlling large arrays of gate-defined quantum devices. The method uses a novel, on-chip, multiplexed charge-locking system and helps to overcome the restraints imposed by the number of wires available in cryostat measurement systems. Two device innovations are introduced. Firstly, a multiplexer design which uti...
Article
Full-text available
The properties of conductance in one-dimensional (1D) quantum wires are statistically investigated using an array of 256 lithographically-identical split gates, fabricated on a GaAs/AlGaAs heterostructure. All the split gates are measured during a single cooldown under the same conditions. Electron many-body effects give rise to an anomalous featur...
Article
Full-text available
Research in the field of low-temperature electronics is limited by the small number of electrical contacts available on cryogenic set ups. This not only restricts the number of devices that can be fabricated, but also the device and circuit complexity. We present an on-chip multiplexing technique which significantly increases the number of devices...
Article
Full-text available
For 60 years, the Johnson criteria have guided the development of materials and the materials choices for field-effect and bipolar transistor technology. Intrinsic graphene is a semi-metal, precluding transistor applications, but only under lateral bias is a gap opened and transistor action possible. This first application of the Johnson criteria t...
Article
Only a small fraction of contemporary nanoscience will ever emerge as a functioning and commercial nanotechnology. Far too little attention is paid to the hoops and hurdles presented by the transition from science to technology by those who assert that their work will find applications. A systematic protocol is developed for appropriate investigati...
Article
As an implementation of the static random access memory (SRAM), the tunnelling SRAM (TSRAM) uses the negative differential resistance of resonant (interband) tunnelling diodes (R(I)TDs) and potentially offers improved standby power dissipation and integration density compared with the conventional CMOS SRAM. TSRAM has not yet been realised with a u...
Article
Full-text available
We present a multiplexing scheme for the measurement of large numbers of mesoscopic devices in cryogenic systems. The multiplexer is used to contact an array of 256 split gates on a GaAs/AlGaAs heterostructure, in which each split gate can be measured individually. The low-temperature conductance of split-gate devices is governed by quantum mechani...
Chapter
In this chapter, the author considers the borderline between manufacturability and unmanufacturability, and then examines the consequences on nanoelectronic device performance. As present, there are two distinct routes to manufacture of nanoscale artefacts. The dominant route is top-down, sculpting and adding selective volumes of materials to a sta...
Article
Fifty years after tunnelling through semiconductor heterojunctions was originally investigated, the present authors are the first to demonstrate the required reproducibility, in wafer, between wafers in a given growth run, and from run to run, of the electrical properties required for manufacturing a microwave and millimetre-wave detector based on...
Article
Electron tunnelling through semiconductor tunnel barriers is exponentially sensitive to the thickness of the barrier layer, and in the most common system, the AlAs tunnel barrier in GaAs, a one monolayer variation in thickness results in a 300% variation in the tunnelling current for a fixed bias voltage. We use this degree of sensitivity to demons...
Article
Tunnel currents through semiconductor tunnel barriers have proved very difficult to control to the extent that device-to-device variability and wafer-to-wafer irreproducibility have prevented electronic devices based on tunnelling from ever going into production. With reference to a single tunnel barrier of AlAs in a GaAs multilayer structure with...
Article
The first Fellows of the Royal Society with connections to New Zealand were James Cook, Joseph Banks and Daniel Solander, all of whom came to the South Pacific in 1769 to observe the transit of Venus. They subsequently made contact with New Zealand Māori, mapped the islands of New Zealand, and made many scientific observations. Since 1879, 42 New Z...
Article
Full-text available
Thin-film electronics in its myriad forms has underpinned much of the technological innovation in the fields of displays, sensors, and energy conversion over the past four decades. This technology also forms the basis of flexible electronics. Here we review the current status of flexible electronics and attempt to predict the future promise of thes...
Article
Tunneling SRAM (TSRAM) based on the resonant tunneling diodes (RTD's) [1] potentially offers seven orders of magnitude lower standby power and four times higher integration density compared to conventional CMOS SRAM and has enormous potential for post-CMOS scaled circuits [2], [3]. TSRAM has not yet been realized with a useful bit capacity mainly b...
Article
Between a promising initial result in a laboratory and the commercial availability of a product there are many hoops to jump through, and indeed there is a severe attrition rate so that few results actually make it to products. In this article, I want to focus on the technical aspects of achieving a manufacturable prototype, but it must be remember...
Conference Paper
Much of nanoelectronics today does not pass the tests for nanomanufacture - achievement of high yields to a pre-specified performance and tight tolerance - and so will not become a nanotechnology with its implication of engineering control. Seven out of a very wide range of examples are given where the electronic or optical properties of nanostruct...
Article
Although small structures can be fabricated by deposition, lithography and etching, in some cases their intrinsic variability precludes their use as elements in useful arrays. Manufacture is a proper subset of fabrication. We show that structures with 3 nm design rules can be fabricated but not manufactured in a top-down approach—they do not have t...
Article
As a novel implementation of the static random access memory (SRAM), tunneling SRAM (TSRAM) uses a resonant- tunneling-diode (RTD)-based monostable-bistable logic element (MOBILE) and features low standby power dissipation and high integration density. A major challenge in TSRAM's low-cost manufacture is the wide current variability associated with...
Article
Full-text available
Just under half of all energy consumption in the UK today takes place indoors, and over a quarter within our homes. The challenges associated with energy security, climate change and sustainable consumption will be overcome or lost in our existing buildings. A background analysis, and the scale of the engineering challenge for the next three to fou...
Article
We study the yield and reproducibility of quantized conductance in short one-dimensional quantum wires in split-gate transistors. In order to get an unambiguous assessment, more than 500 split gates have been fabricated and tested at 1.4 K. The study clearly shows that the devices are too sensitive to the inherent dopant structures and to variation...
Article
Measurements of current-voltage characteristics of the wide gap semiconductor devices using power electrical pulses can induce damage of the devices due to Joule heating. In our experiments the 4H-SiC sample and the GaN Gunn diode were placed in series to the transmission line, and a gauge resistor as used for the determination of incident pulse am...
Article
The multi-surface gate architecture was applied to a small lateral single quantum dot (QD). By employing ultrasonic agitation development, we tried to work out a reliable fabrication scheme for closely-spaced quantum dots, and then tested yield by measuring Coulomb blockade of QD at 300 mK. The yield results (less than 50%) show such a fabrication...
Article
Full-text available
We have investigated the fabrication and operation of high power GaN Gunn diodes. The Gunn effect (intervalley electron transfer giving rise to N-type negative differential resistance (NDR)) in n-doped GaN material has been simulated with a three valley analytical model, and it is shown that the effect is expected to occur at fields in excess of 20...
Article
Measurements of volt-ampere characteristics of a nitride and carbide wide gap semiconductor devices using power electrical pulses of nanosecond duration eliminate Joule heating of the devices. However the devices operating at high electric field and having structures of nanometer size may be damaged by short electrical pulses due to consequence of...
Article
Full-text available
Beyond the double barrier diode as the paradigm of resonant tunnelling, a range of novel tunnelling phenomena have been investigated with judiciously designed multilayer semiconductor structures. We describe three such examples: tunnelling between two superlattices, tunnelling through indirect gap semiconductor layers, and the optical detection of...
Article
The engineering of tunnel barriers has not yet succeeded to the point where low cost high volume manufacture of tunnel devices can be undertaken. We analyse one overriding reason for the unacceptable variability in device performance and suggest that engineered tunnel barriers are unlikely to play a role in extending the CMOS Roadmap, as has recent...
Article
If split-gate devices are to be used in practical applications, such as metrology, the ability to fabricate devices with closely identical electronic properties is essential. The alternative is to treat each device as a one-off, and undertake extensive calibrations as a prelude to use. In this paper we describe initial results using standard proces...
Article
We investigate the potential of ion implantation being used to isolate multilayer semiconductor devices that have been grown epitaxially one above the other. It is proposed that such a novel procedure will enable vertical device integration and lead to an improvement in the density of devices per unit area of wafer surface, and also offer new circu...
Article
Full-text available
In pursuit of p-type doping, we have implanted GaN with Mg ions at 200 and 500 keV with the substrate temperature maintained at -150 (cold) or +300 degrees C (hot) during ion irradiation. The samples have been annealed at 1000 degrees C postion implantation. The radiation damage peak position (and its profile), the dopant distribution, and the dama...
Article
We have implanted GaN with Mg ions over an energy range of 200keV to 1MeV at substrate temperatures of -150 (cold) and +300 deg. C (hot). The radiation damage formation in GaN was increased for cold implants when compared to samples implanted at elevated temperatures. The increase in damage formation is due to a reduction in the dynamic defect anne...
Article
Given the superior control of ion implantation over dopant incorporation during epitaxy, in addition to the throughput and hence cost advantages, we have attempted the design and fabrication of a GaAs planar-doped-barrier diode with pre-specified electrical properties, using a fully ion implanted fabrication technology. The process requirements for...