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PhD in Engineering - Integrated Germanium-Tin Photodetectors for Optical Communication and Quantum Applications

   College of Science and Engineering

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  Dr R Millar, Prof D Paul  No more applications being accepted  Competition Funded PhD Project (European/UK Students Only)

About the Project


In this fully funded PhD project (3.5 years) you will use state-of-the-art nanofabrication facilities to develop avalanche photodiodes and single photon avalanche diode detectors operating at 2 µm wavelength for fibre-optic communication systems, as well as quantum encryption, sensing, and biomedical applications. The work will involve simulation, fabrication and characterisation and there will be flexibility in which area you want to focus on.


Big data, and exponentially growing internet traffic means that we are reaching a bandwidth bottleneck in data centres and over fibre networks. For decades now, optical fibre has been used to transmit data encoded in pulses of light, as optical communications is high-bandwidth, low loss and low energy compared to electrical networks. Wavelengths of 𝜆 = 1.31 µm and 𝜆 = 1.55 µm are commonly used due to low optical losses (< 1 dB per kilometre), and the availability of optical amplifiers. Current technologies, however, cannot sustain the huge growth in internet protocol (IP) traffic, as networked devices and the Internet of Things (IoT) become ever more ubiquitous. New solutions are required, and extending optical communication windows to the 2 µm waveband can potentially dramatically increase bandwidth and facilitate the growth of big data applications. 

For a scalable solution, the photodetectors used to receive these optical signals must be low cost, and easily integrable with CMOS electronics. A novel Group IV alloy comprised of Germanium and Tin (GeSn) can absorb strongly at these wavelengths, and is compatible with Si foundry growth and processing meaning it can be mass produced at low cost, i.e. using the same techniques used to make CMOS electronics. This makes it an ideal material to create highly sensitive avalanche photodiodes (APD), and single photon avalanche diode (SPAD) detectors, to support the establishment of the 2 µm communications band. SPAD devices can time the arrival of single photons of light, and can be used for Quantum Key Distribution (QKD) – using quantum properties of light to unbreakably encrypt our communication protocols. The 2 µm waveband can enable long-range free-space communication with satellites, or over hollow-core photonic-crystal fibre. Low-cost detectors operating at ~ 2 µm can also be used for imaging applications in astronomy, as well as for detection of CO2, H2O and CH4 molecules, and for imaging through biological tissue in healthcare applications.

Project details

In your PhD, you will use finite element modelling packages to design GeSn detectors integrated with Si photonics platforms. You will have access to the state-of-the-art James Watt Nanofabrication Centre; a 1400 m2 facility with over £35 M worth of capital equipment, where you will fabricate GeSn detectors before testing them in optics laboratories. 

The work will be a collaboration between Dr Ross Millar, and Prof Douglas Paul (Semiconductor Devices Group), and will contribute to Dr Millar’s Royal Academy of Engineering fellowship (https://www.raeng.org.uk/news/news-releases/2019/august/academy-supports-engineering-excellence-with-18-ne) and work with Heriot-Watt University and the University of Bristol. Within the research group there is also collaborative research with further industrial partners including Toshiba Europe, Sivers Photonics, Jaguar Land Rover, Horiba-Mira, IQE and many others, meaning you will have opportunities to liaise with external industrial and academic collaborators. You will likely have an insight into the process of intellectual property and patent generation, either with commercialisation of previously submitted patents, or newly generated IP.

In completing the PhD project, you will develop a range of skills that will enable you to have a career in either academia or industry. This will include; nano-fabrication, vacuum systems, optics, integrated photonics, RF electrical measurements and a range of simulation techniques.

Applicant requirements

The ideal candidate will have a background in engineering, physics or chemistry, with background knowledge of semiconductor physics. No prior nano-fabrication experience is required. Experience of programming will also be beneficial to the project, but is not essential. You must be self-motivated, have good interpersonal skills, and be interested in conducting interdisciplinary work that combines theory, simulation, fabrication and characterisation.

How to Apply: Please refer to the following website for details on how to apply:


Funding Notes

Funding is available to cover tuition fees for UK/EU applicants for 3.5 years, as well as paying a stipend at the Research Council rate (estimated £16,062 for session 2022-23).
There will be opportunities to supplement your stipend with paid tutoring and demonstrating work.
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