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PhD Opportunities

I welcome enquires at all times from suitable candidates, which include anyone who has a minimum Bachelors degree of 2.1 (UK) or international equivalent qualifications. You should have an interest or experience in experimental engineering/chemistry/physics.

If you fit into this description, please read the areas of research below and contact me (vishal.shah@warwick.ac.uk) with a CV to arrange an informal chat. Depending on the time of year, there may be other funding mechanisms available for UK/EU or international students; I encourage you to search for these alongside making informal queries.

Defects and their effect of reliability for Silicon Carbide power devicesLink opens in a new window

Funding available for PhD studentship for Oct 2022 or Jan 2023 start - funding for international students now available. Students must have a minimum Bachelors degree of 2.1 (UK) or international equivalent qualifications and a degree in experimental engineering/chemistry/physics, with experience in semiconductors.

Additional Supervisors: Dr Oliver Fox (Diamond Light Source Ltd) & Dr Tamzin Lafford (Bruker UK Ltd)

Wide bandgap (WBG) semiconductor materials, such as Silicon Carbide (SiC) and Gallium Nitride (GaN), have recently been introduced into the power electronics market, with early adoption of SiC devices in hybrid and fully electric cars being the main driver of industrial uptake. Predictions state that the market will be worth $2bn by 2024 and of direct relevance to achieving the UK’s net zero commitment.

A major issue for SiC power electronic devices is long-term reliability due to intrinsic extended defects, e.g. the presence of basal plane dislocations in the starting substrate. In a critical area, these defects drastically reduce device long-term reliability. An in-depth study of extended defects in WBG materials and devices is key to mitigating their effects.

This studentship will expand on recent collaborative work between the University of Warwick, Bruker UK Ltd. and Diamond Light Source which has begun to develop techniques for transmission, surface and cross-sectional imaging of defects in research and commercial off the shelf material and devices. The studentship will involve the study of SiC materials from device fabrication facilities in the power electronics group (PEATER) at the University of Warwick, lab based non-destructive X-ray diffraction imaging (XRDI) at Bruker Ltd. and synchrotron white beam XRDI (SWB-XRDI) at the B16 Beamline at DLS. Dr Shah is at the forefront of WBG power materials research in the UK while B16 is a leader in synchrotron XRDI and Bruker has several decades experience developing leading-edge XRDI tools for lab and industry.

The proposed studentship will build on the existing SWB-XRDI capability at B16 and will 1) optimise XRDI techniques for defect detection and classification, 2) investigate WBG defect correlation and classification compared to other techniques, 3) develop in-situ high electrical current density, UV light and thermal stressing on-chip to investigate the real-time defect dynamics within research and commercial devices, and 4) study the correlation of defect with electrical results and develop defect mitigation strategies.

Applications are open, contact Dr Shah (vishal.shah@warwick.ac.uk).

3C-SiC - the renaissance of a wide bandgap material (x2 projects available)

3C-SiC is a material which has potential as a replacement for 4H-SiC, due to its ability to be epitaxially grown on cheaper Silicon substrates, whilst having better largely reducing material costs. Furthermore compared to 4H-SiC, 3C-SiC has a potential larger mobility and a the larger conduction band offset at the 3C-SiC/SiO2 interface theoretically enables MOS devices to have considerably lower leakage currents and interfacial charge levels than unipolar MOS devices fabricated on 4H-SiC.

However, the large mismatch in physical, thermal and crystallographic properties between 3C-SiC and the underlying Si substrate hampers the development of this material due to the larger defect levels in the material. Even though high mobility 3C-SiC MOSFETs have been reported in the past decade, in-depth studies of 3C-SiC MOS devices still show high leakage levels and positive charge at the 3C-SiC/SiO2 interface.

There are two projects in this area:

  1. New processing techniques will be developed at Warwick to address these materials issues and will be implemented in a 3C-SiC power electronics device.
  1. The student will develop SiC materials and fabrication methodologies to contribute to micro electronic mechanical systems (MEMS) structures for power devices and sensors

Applications are open and rolling throughout the year, contact Dr Shah in the first instance (vishal.shah@warwick.ac.uk).

Doping and Semi-insulating Silicon Carbide for RF devices

Whilst the high voltage area is obvious to the future of SiC, it’s frequency capability is only assumed to be low (< 500 MHz). There is a serious application of wireless power transmission within the lower part of the RF energy spectrum, in the 1MHz to 3GHz range and in the >50V 1kW+ application space which could be utilised if SiC platforms are developed.

These include magnetron replacement, industrial heating and drying, RF plasma lighting and other applications, etc. In the long term, this material is through to be suitable for application in high power (>1000W), medium distance (>10m to 1km), microwave wireless power transfer (WPT) which is power dense (>1kW/m2) and highly directional. It has the potential to introduce a new generation of disruptive technologies in a number of applications including Internet of Things (IoT) sensor networks and wireless charging of electric vehicles (EVs)

The aim for this studentship would be to develop semi-insulating doping in both 4H-SiC homoepitaxy and 3C-SiC on Si heteroepitaxy, using the UK’s only industrial SiC CVD at the University of Warwick, for use as a platform for RF devices. Certain elemental species in SiC are amphoteric where only low levels (<1e17cm-3) can create semi-insulating (SI) layers (ρ >1e9 Ω-cm). The reasoning for this is to increase the monolithic integration of RF and power electronics both Si and SiC commercial substrates. This would fit into the research priority of “Manufacturing of compound semiconductors (CS) and CS on Silicon (epitaxy, fabrication and process control).”

Specifically in this studentship, both implantation and epitaxy of amphoteric will be developed, in order to demonstrate semi-insulating SiC materials. The student will learn epitaxy, materials characterisation, device simulation and device fabrication. They will design experiments and process samples in our epitaxial and cleanroom facility, which includes state-of-the-art thin film deposition, atomic layer deposition, annealing furnaces, and lithographic facilities. They will also learn characterisation techniques such as electrical measurements (e.g. IV, CV, Hall measurement, DLTS, high voltage measurements), physical measurements (e.g. SEM, TEM, AFM, XRD). Indeed, they may also help to develop new characterisation techniques like c-AFM or XRT with partners or using national facilities (e.g. Diamond Light Source).

Applications are open and rolling throughout the year, contact Dr Shah in the first instance (vishal.shah@warwick.ac.uk).

Propose your own

I am happy for students to propose any subjects in the wide bandgap semiconductor area to do with: material fabrication, materials characterisation, device fabrication techniques, electrical characterisation or new functionalisation (sensors, quantum, chemical processing, harsh environment electronics etc). Please get in touch!