Prof Douglas J. Paul > PhD Projects

Below are currently available PhD projects where Prof Paul is actively looking for PhD students to undertake research. For U.K. and European Union students, the department has a large number of EPSRC Doctoral Training Awards, Centre for Doctoral Training in Integrative Sensing and Measurement and Photonics Integration and Advanced Data Storage, subject to availability and the quality of the applicant, funding is available for high quality students.

Most of the projects will be collaborative with UK or European universities and companies. All of Prof Paul's students also regularly present their research at the major internation conferences in their fields across the globe.

A number of scholarships and funded PhD positions may also be available for high quality oversees students. Applicants should have a degree in physics, applied physics, electrical and electronic engineering or a related subject. All the projects involve students fabricating their own devices in the James Watt Nanofabrication Centre at Glasgow and testing their devices.

Details of how to apply for a PhD can be found on the Graduate Studies Application Web Pages

 

MicroCrystal Silicon and Germanium Single Photon Avalanche Detectors

Whilst CMOS single photon avalanche detectors (SPADs) are commercially available, the quantum efficiency is limited by the indirect bandgap and the thickness of the absorption region. At near infrared wavelengths where automotive rangefinding and LIDAR can most easily operate through fog and rain, expensive InGaAs technology limits large SPAD arrays for civilian applications. Such single photon detectors are essential for many quantum optics experiments but also for quantum communications, squeezed light imaging, rangefinding, LIDAR and appealing at longer wavelengths for the optical assessment of breast cancer risk. This project aims to deliver silicon CMOS SPADs with 80% single photon detection efficiency in the visible and Ge on Si SPADs for 1500 to 1600 nm operation for automotive and autonomous vehicle LIDAR. By growing either Si or Ge microcrystals on top of microfabricated Si pillars, thick absorption regions with very low defect densities can be achieved, ideal for high performance photodetectors. The project is funded through the EC H2020 FET Project "MicroSPIRE" and is a collaboration beween the University of Glasgow and the Politecnico di Milano in Italy, the University of Milano-Bicocca in Italy, the Philipps University Marburg in Germany, the Technical University of Dresden in Germany and Micro Photon Devices in Italy.

The University of Glasgow is seeking a high quality PhD student to fabricate the CMOS and Ge on Si devices and aid with the characterisation of the devices in collaboration with the European partners of the project. The successful student will work in the James Watt Nanofabrication Centre and learn micro and nanofabrication skills alongside academic colleagues and industrial engineers. The student will also learn about single photon detectors and photonic devices. The PhD position available includes both an annual stipend (not less than £14,553 tax free) and the payment of the university fees.

 

A Single Chip Atomic Clock

Atomic clocks are the most accurate timing system yet developed. They are used as timing standards essential for the internet and communications but also are essential for navigation and part of the key technology in satellites for GPS navigation. There are many other potential applications for financial trading and GPS-free personal navigation if a cheap, practical, miniature atomic clock can be realised. The US National Institute for Standards and Technology developed a chip scale atomic clock in the 2000s which has an accuracy of nanoseconds using a heated rubidium vapour in a miniature gas cell whose accuracy is limited by the velocity of the atoms in the gas through Doppler broadening.

This project has the aim of producing a single chip cold atom atomic clock where lasers are used to Doppler cool atoms to milliKelvin temperatures to enable a chip scale atomic clock with a sub-picosecond accuracy. This is an improvement by 3 orders of magnitude over any demonstrated chip scale clock. The project will integrate diode lasers with integrated waveguides, a Micromechanical Mechanical Electrical Microsystem (MEMS) gas cell, photodetectors, grating magneto-optical traps and high Q resonators to deliver an atomic clock.

The student should have an undergraduate degree in Physics, Electrical and Electronic Engineering or an equivalent degree. They will design and model devices and be working in the James Watt Nanofabrication Centre to fabricate the clocks before testing the devices. The work will be collaborative with the companies M Squared Lasers, Kelvin Nanotechnology and Optocap as part of an InnovateUK Quantum Technology project.

 

Squeezed Light Interferometer for Measuring Gravity

Work at the University of Glasgow published in Nature and reported on the BBC news has already taken a silicon mass on a spring fabricated using the same Micro- Electro Mechanical System (MEMS) technology to the gyroscope in all smart phones that determine orientation and improved the sensitivity by a factor of 5000. This MEMS gravimeter has the potential to be used to search for new oil & gas researches, find buried utilities quickly thereby reducing roadworks and provide an early warning for volcanic eruptions. This project aims to deliver a quantum squeezed light source with pairs of correlated photons that can be used to measure the output of the MEMS gravimeter to improve the sensitivity by up to a factor of 40. The project also involves developing Ge photodetectors that can detect single photons which also has applications of rangefinding and LIDAR (determining how far away objects are by bouncing photons off them and timing their return) at wavelengths of light that can see through rain, mist and fog. A Michelson interferometer will be developed in a silicon chip using four wave mixing for the squeezed light source, a beam splitter and Ge photodetectors where the silicon proof mass is the moving mirror in the interferometer to enable squeezed light measurement of the displacement.

The project is in collaboration with Optocap and IQE as part of an InnovateUK project. The successful student should have an undergraduate degree in Physics, Electronic and Electrical Engineering or an equivalent subject. They will design and model the interferometer and be working in the James Watt Nanofabrication Centre to fabricate the sensors before testing the devices.

 

Short Wave Infrared Ge on Si Single Photon Avalanche Detectors for Automotive and Autonomous Vehicle LIDAR

Time correlated single photon detection enables a photon to be sent and the time it takes to return to be recorded. From this measurement and knowing the speed of light, the distance the photon has travelled can be calculated which is a technique known as rangefinding or LIght Detection And Ranging (LIDAR). There are many applications of rangefinding which include 3D imaging and seeing around corners but also it is a key technology for the navigation of autonomous vehicles so they do not bump into objects around them. Rangefinders are also important for road vehicles and one major application in the automotive industry is for sensors to determine if a car might crash so that the driver can be warned or preventative measures can be undertaken. The technology could also be used in digital and mobile phone cameras for autofocusing.

This project aims to develop the key device required for rangefinding at the important eye-safe wavelengths of 1.55 µm but also investigate longer wavelengths where the technology could be used for direct gas identification and imaging. The project will involve designing Ge and GeSn materials on a silicon substrate as the absorber layers for single photon detectors before fabricating a range of different single photon detectors and then testing them. At present all room temperature commercially available single photon detectors at this wavelength rely on expensive InGaAs technology which is too expensive for consumer markets and has US export controls. This project is aiming to develop much cheaper technology on a silicon platform that could be mass produced in silicon foundries.

The student should have an undergraduate degree in Physics, Electrical and Electronic Engineering or an equivalent degree. They will design and model devices and be working in the James Watt Nanofabrication Centre to fabricate the devices before testing the photodetectors. The project is in collaboration with the companies Optocap and IQE as part of an InnovateUK project.

 

Terahertz Ge/SiGe Quantum Cascade Lasers on Silicon Substrates

The terahertz region of the electromagnetic spectrum (0.3 THz to 10 THz) is being investigated for medical imaging (oncology including skin cancer and breast cancer diagnosis), security screening and non-destructive test in the pharmaceuticals industry. At present all the available coherent sources are high cost or require cryogenic operation such as the GaAs THz quantum cascade laser (QCL) where polar optical phonon scattering limits the operation to low temperatures. Unlike interband lasers where the indirect bandgaps of silicon and germanium prevent lasing, QCLs are unipolar lasers which only use intersubband transitions inside quantum wells to enable lasers. In group IV materials such as silicon and germanium unlike III-Vs or II-VIs, there is no polar optical phonon scattering and experiments have demonstrated long non-radiative lifetimes that are relatively temperature independent ideal for a THz laser at room temperature. Glasgow is part of an EC H2020 Future Emerging Technologies project with Roma Tre University in Italy, ETH Zurich in Switzerland, IHP in Germany and Nextnano in Germany. The aim is to produce a THz Ge/SiGe QCL operating at room temperature using Ge quantum wells and SiGe barriers grown directly on top of silicon substrates.

The successful student should have an undergraduate degree in Physics, Electronic and Electrical Engineering or an equivalent subject. They will design and model structures for LEDS, tunnel diodes, optically pumped lasers and QCLs and be working in the James Watt Nanofabrication Centre to fabricate the devices before testing them electrically and in FTIR systems.

 

Microfabricated ion traps with integrated optical control for atomic clocks and quantum computers

Microfabricated devices for the confinement and exquisite control of atomic particles are set to feature as essential core components in a range of quantum-enabled instrumentation. Applications of these devices are in atomic clocks and sensors, for use in precision positioning, navigation and timing. Furthermore, these chip-scale devices will be used for research in high-precision quantum metrology and have been proposed as a building block for quantum simulators and quantum computers. The aim of this project is to develop next-generation devices with enhanced performance characteristics, well-suited to these applications.

The UK's National Physical Laboratory (NPL) has developed novel chip-scale ion traps which are made using advanced microfabrication techniques, with the facilities at Glasgow's James Watt Nanofabrication Centre (JWNC). The microtrap device is a MEMS structure which, under the application of a radiofrequency high voltage, creates a linear array of segmented trapping potentials for storing strings of atomic ions. Irradiation by laser light cools the ions and controls their behaviour. Uniquely, the device combines a 3D structure with a parallel fabrication process, to exhibit a set of operating characteristics that is highly desirable for applications in atomic quantum technology.

At present all ion traps have bulk optical components for the laser cooling and optical control of the ions. This project has the aim to develop integrated optical components for laser cooling and the control of the quantum states of the ions in the taps. This will require the development of integrated on-chip laser delivery into the traps and providing high Q optical cavities to allow control of the quantum properties of single and multiple interacting ions in the traps.

Research and development in the microfabrication process will be conducted in the James Watt Nanofabrication Centre. Testing and application of devices will be performed in partnership with NPL in Teddington, London thus providing a secondment opportunity.

 

Mid Infrared Sensing using Non-Linear Silicon Photonics Technology

Non-linear photonic materials are essential to allow mixing for frequency up and down conversion along with parametric gain. Silicon being a centro symmetrical material has a weak χ(2) optical parameter and is therefore a poor non-linear photonic material. Recent work at Glasgow has shown that tensile strains up to 2.5% can be applied to silicon waveguides thereby changing the crystalline lattice from cubic to tetragonal and thereby producing a large χ(2) non-linearity. This project has the aim for producing a strong χ(2) in silicon waveguides and using this to demonstrate the mixing of two off-chip lasers to produce a mid-infrared source and detector using second harmonic generation with periodically poled silicon photonic technology. The project will also aim to produce in silicon technology for the first time phase modulators using the process induced strain. The devices to be developed have applications in telecoms but also a wide range of mid-infrared sensing technologies for pollution monitoring, safety systems and healthcare. The technology also allows the production of entangled single photon pairs for secure quantum communications. The project is ideal for a student with a background in physics, electronic engineering or materials science.

 

Mid-infrared explosives and healthcare sensors

Plasmons are the quantum quasi-particle formed from the oscillations of electrons in a metal with respect to the fixed positive ions. When plasmons interact with light they form polaritons and the combined plasmon-polaritons can be used to amplify the absorption fingerprints of molecules leading to sensors that can identify different molecules. This identification of molecules has many applications for gas detectors, environmental monitoring (e.g. measuring carbon dioxide and pollutants), security detectors (e.g. detection of explosives or bioweapons) and healthcare detectors (e.g. early stage oncology detection). The molecular absorption fingerprint lines from most of the interesting molecules for the above applications lie in the mid-infrared so cheap and practical sources of radiation and detectors are not readily available despite the enormous potential.

Work at Glasgow has already demonstrated mid-infrared detection and identification of explosives using heavily doped n-Ge plasmonic antennas on a silicon substrate (Nano Letters 15(11), pp. 7225 - 7231 (2015) - DOI: 10.1021/acs.nanolett.5b03247). The technology has the potential to be mass produced cheaply in silicon foundries and operates best in the mid-infrared. This project has the aim of integrating detectors and non-linear mixing elements to develop complete sensors that just require a mid-infrared source such as a quantum cascade laser or a cheap blackbody heater. Heterostructures of Ge/SiGe to form Ge quantum wells will be used for intersubband detection of the mid-infrared radiation and by coupling the light to the anti-crossings in the quantum wells, non-linear interactions will be generated that will tune the detection wavelength thereby allowing tunable detection of many different molecular bonds at different wavelengths.

The student should have an undergraduate degree in Physics, Electronic and Electrical Engineering or an equivalent subject. They will design and model devices and be working in the James Watt Nanofabrication Centre to fabricate the sensors before testing the devices.

 

Atomic Magnetometers for Magnetospinography Assessment of Nervous System Diseases

The ability to detect small magnetic fields has many applications and in the medical field superconducting SQUID based detectors have demonstrated the ability to monitor brain and nerve activity suitable for the study and diagnosis of a wide range of diseases. Such superconducting devices have significant limitations mainly relating to their cryogenic operation requirement which also limits the lateral resolution of the imaging technique. For spinal cord or nerve imaging in arms and hands, the total imaging area may only be a few mm to a cm wide and so sufficient resolution is required to image such biological systems. More recently a number of groups have demonstrated the use of optical probing of the spin states of atoms in gases to be able to detect changes in magnetic field down to femtoTesla (1 part in 10^15) levels. This project aims to deliver Rb atoms in a MEMS fabricated cell with integrated 780 nm DFB lasers and silicon photodetectors to deliver a multipixel magnetometer imaging array suitable for a range of applications including magnetospinography applications. The work will be in collaboration with the School of Medicine in Glasgow and the School of Physics in Strathclyde University.

The successful student should have an undergraduate degree in Physics, Electronic and Electrical Engineering or an equivalent subject. They will design and model the interferometer and be working in the James Watt Nanofabrication Centre to fabricate the sensors before testing the devices.

 

Single Electron Transistors and Devices

Single electron transistors (SETs) use Coulomb blockade to control the flow of electrons one at a time. While the low gain restricts the use of such devices in circuits, SETs are extremely sensitive charge detectors (electrometers). Therefore SETs can be used to probe small molecules or electron transport in small transistors. Further applications include a new current standard, the non-invasive detection of quantum states for the read out in quantum computation and the detection and imaging of objects through wall for security applications. This project will involve designing, fabricating and testing a number of different types of SETs using silicon technology and using them to probe both small MOSFETs and small molecules. The project will use the high resolution electron beam lithography and RIE etch facilities in the James Watt Nanofabrication Centre to produce SETs with dimensions below 5 nm in size allowing room temperature operation of the electrometers. The project is ideal for a student with a background in physics, electronic engineering or materials science.

 

Germanium / Germanium Tin Light Sources and Detectors

At present there are extremely few compact semiconductor photodetectors, LEDs or lasers which operate between 2 and 5 microns wavelength. This part of the electromagnetic spectrum has potential applications for healthcare (spectroscopy of blood analytes) and pollution monitoring (CO, CO2, NO, N2O and HCl). For these applications, low cost systems, preferably on silicon substrates would allow optical lab-on-a-chip for multiple applications where the electronics and communication systems could be monolithically integrated. Such systems could be ultimately put into autonomous sensors for remote monitoring with many new markets in healthcare, security and environmental monitoring benefitting from the technology.

This project is aimed at producing photodetectors, LEDs and lasers using germanium and germanium tin grown on top of silicon. Germanium has an indirect bandgap at room temperature of 1.89 µm and this can be increased through the application of tensile strain. We have already demonstrated the use of process induced strain to produce Ge on Si material with a direct bandgap beyond 2.2 µm. This project will build on this work and develop photodetectors and LEDs for operation above 2 µm using process induced strain and similar technology to allow sources and detectors of light to be integrated on a single silicon chip. The final part of the project will investigate and attempt to make the first direct bandgap lasers on a silicon substrate operating at room temperature.

 

Ultralow Voltage Switches

The silicon transistor circuits on microprocessors and memory of the microelectronics industry have had an enormous technological, social and economic impact on the world. The number of transistors has increased by such large numbers that now 2 to 5% of all energy consumption is in powering Information Communication Technology systems. Reducing the power consumption of MOSFETs has been accomplished for the last 40 years by scaling the transistor to smaller dimensions, the economics of which are described by Moore’s law. The present 22 nm length scales of MOSFETs make further scaling to reduce power difficult if not impossible due to the non-scaling supply voltage of the transistor. The present supply voltage of around 1 V cannot be substantially reduced without signal-to-noise ratio in circuits being compromised significantly.

This project is aimed at producing a new type of transistor with a supply voltage of 0.2 V. The device is a unipolar device which uses bandgap engineer to engineer the threshold voltages to below 0.2 V whilst maintaining a low off current. Such a reduction in supply voltage corresponds to a 125 reduction in power dissipation for a switch which is the building block of all digital microelectronic circuits. The technology could be used in the mainstream microprocessors or for ultra low power devices that are being proposed for self-powered autonomous sensing applications using energy harvesting power sources such as healthcare, security and remote environmental sensing.

 

If you are interested in any of these projects or research areas then please contact: Douglas.Paul@glas gow.ac.uk

All applications for a PhD with Prof Paul must be through the Graduate Studies Application Web Pages.