Welcome to the Impact Ionisation Group

Ongoing projects

Grant title Investigators DatesFunding body
Knowledge exchange in AlGaAs X-ray detectors J S Ng, C H Tan, & J P R DavidJul 09 - Jun 12 STFC (PIPSS)
Extended Temperature OptoElectronics II (ETOE II) J P R David, J S Ng, C H Tan, & K M Groom Oct 08 - Sept 11TSB
Materials for avalanche receiver for ultimate sensitivity (MARISE) J S Ng, J P R David, & C H Tan May 08 - Apr 11EU FP7
New high-performance avalanche photodiodes based on the unique properties of dilute nitrides J P R David, J S Ng, C H Tan, & M Hopkinson May 08 - Apr 10EPSRC
Infrared photodiodes based on Type-II Superlattices J P R David, C H Tan, & J S NgApr 07 - Mar 10 EMRS DTC
Royal Society University Research Fellowship J S NgOct 06 - Sept 11Royal Society
Ultra high detectivity single carrier multiplication InAs avalanche photodiodes for IR optical detection C H Tan, J P David and J S Ng Oct 2010 - Sept 2013 EPSRC
  • Knowledge exchange in AlGaAs X-ray detectors, Jul 09 - Jun 12, STFC
    • Sheffield investigators: J S Ng, C H Tan, & J P R David
    • Project partner: University of Leicester (led by Dr John Lees)
    • Brief project descriptions:
      • The ideal detector for X-ray spectroscopy imaging system would have 100% detection efficiency, spatial resolution of a few microns, and spectral resolution of a few eV. It should also have low power consumption and be able to operate over a wide range of temperatures and in demanding radiation environments. In contrast, available Silicon X-ray detectors have low radiation tolerance limitations and demand thermal cooling for X-ray spectroscopy. Hence there is a need for detectors that have good spatial and energy resolution, good radiation tolerance and can operate at or above room temperature without the need for external cooling.
      • New detectors based on wide bandgap (> 2 eV) semiconductor materials have potentials to overcome the spectroscopic, temperature, radiation and voltage limitations of silicon. AlGaAs is one such material and detectors based on this material could find applications in areas such as medical and small animal imaging, real time extremity dosimetry as well as environmental monitoring such as X-ray fluorescence analysis of oil contaminates. AlGaAs detectors should also be able to operate in harsh radiation environments such as those associated with oil exploration and volcanic studies as well as future planetary missions and/or landers.
      • The two academic groups (Space Instrumentation Group, University of Leicester and the Avalanche Photodiode Group, University of Sheffield) have been exploring the use of wide band gap semiconductors for use as X-ray photon counting detectors. The Leicester - Sheffield collaboration pioneered use of AlGaAs sensors as room temperature X-ray detectors, and they are continuing to improve their performance. The project has a third partner, Centronic Limited, which is a SME with a wide portfolio in radiation detectors for a range of demanding applications.
      • A successful project will produce sensors that have applications in many areas, with potential benefits for healthcare in the UK (through better medical sensors) and environment studies.
  • Extended Temperature OptoElectronics II (ETOE II), Oct 08 - Sept 11, TSB
    • Sheffield investigators: J P R David, J S Ng, C H Tan, & K M Groom
    • Project partners: CIP Technologies (consortium coordinator), Oclaro, SAFC Hitech, Loughborough Surface Analysis, and University of Surrey.
    • Brief project descriptions:
      • For ETOE II: The new project has two main thrusts: the development of reliable aluminium-containing active photonic devices and, longer term, to look at alternative active layer materials for InP and GaAs devices, including nitrogen, antimony and bismuth. Consortium contributions include: metal-organic vapour phase epitaxy (MOVPE) growth from novel precursors for the in-situ etching of aluminium-containing materials by SAFC Hitech; layer growth from Oclaro, CIP and Sheffield; structural design and modelling from Oclaro, CIP and Surrey; device fabrication at Oclaro and CIP; and process characterisation by LSA, Sheffield and Surrey.
  • Materials for avalanche receiver for ultimate sensitivity (MARISE), May 08 - Apr 11, EU FP7
    • Sheffield investigators: J S Ng, J P R David, & C H Tan
    • Project partners: Alcatel-Thales III-V Lab (consortium coordinator), AdvEOtec, IMEC, and id Quantique.
    • Project webpage: http://www.ict-marise.eu/
    • Brief project descriptions:
      • MARISE is to develop innovative engineered APD components with thin avalanche layers to benefit from their promising characteristics likely to advance the present state of the art. MARISE objectives are to push the limits of APDs in: speed and sensitivity.
      • For 10Gb/s access and single photon detection, AlInAs/GaInAs exhibiting low dark current and high responsivity will be developed. The development of a very challenging evanescent waveguide APD structure in the same material system will allow for 40Gb/s operation with a record gain-bandwidth product of 200 GHz.
      • AlGaAs will be combined with a GaInAsN absorber into an innovative, low noise and potentially low cost GaAs-based APD, suitable for 1.3 Ám telecom applications.
  • New high-performance avalanche photodiodes based on the unique properties of dilute nitrides, May 08 - Apr 10, EPSRC
    • Sheffield investigators: J P R David, J S Ng, C H Tan, & M Hopkinson
    • Project partner: University of Surrey (led by Prof Jeremy Allam)
    • Brief project descriptions:
      • To meet the demands of the internet to transmit large volumes of data over long distances, information is sent as short pulses of light. The photodetector which receives this information must have high sensitivity, a fast response, and low levels of 'noise' (random spurious signals). Photodetectors can even be made sensitive enough to detect single photons, and 'photon counting' is an important technique in many applications including sequencing the human genome and quantum computing. Most high-sensitivity photodetectors are semiconductor avalanche photodiodes (APDs): semiconductor materials are robust, cheap, compact, and efficient, while APDs make use of an effect where a very weak signal can trigger a very large current flow (like a single snowflake setting off a massive avalanche of snow). There are many different semiconducting materials, and each is sensitive to a different colour of light or wavelength. While silicon works really well as an APD, it doesn't detect infrared light at the wavelengths needed for optical communications and other applications. We can use combinations of material - one to absorb the light and one to do the avalanche multiplication - but it can be tricky getting the signal across from one material to the other. So APDs are hard to make and therefore expensive.
      • We are going to make new types of APDs with the performance of silicon but sensitive to infrared light, which are also easier/cheaper to make than existing infrared detectors. Firstly, we are going to use a relatively new type of semiconductor (a 'dilute nitride') as the absorbing layer. Dilute nitrides are completely different from other materials: adding a small amount of nitrogen to a conventional semiconductor like gallium arsenide has a huge effect on the properties and can make it sensitive to infrared light. Dilute nitrides even seem to be less noisy than other absorbing layers, since their special properties suppress a source of noise which comes from quantum mechanical tunneling (electrons feel 'heavier' in dilute nitrides and find it harder to tunnel through barriers).
      • Secondly, we are going to replace the conventional multiplication layer made of indium phosphide or gallium arsenide, which compared to multiplication layers made of silicon are rather noisy. The noise comes because multiplication is random: we know the probability that multiplication will occur within a certain time, but not exactly when it will occur. The particular electronic properties of dilute nitrides means that electrons in one energy band (the valance band) can easily trigger avalanches, while electrons in another band (the conduction band) should find it very hard. This situation should lead to very low multiplication noise, perhaps even as low as silicon, and has never been studied before.
      • There is a lot of interesting physics in the movement of electrons in dilute nitride semiconductors, and in the statistics of avalanche multiplication in thin layers. We will use specialized techniques to study these, including squeezing the material under very high pressures to change its properties. This will give us the understanding we need to produce better high-sensitivity light detectors, which are useful for communications, medicine, pollution monitoring, and many other areas that affect our daily lives.
  • Infrared photodiodes based on Type-II Superlattices, Apr 07-Mar 10, EMRS DTC
    • Sheffield investigators: J P R David, C H Tan, & J S Ng
  • Ultra high detectivity single carrier multiplication InAs avalanche photodiodes for IR optical detection, Oct 2010 to Sept 2013
    • Investigators: C H Tan, J P David and J S Ng
    • Post docs: Ian Sandall
    • PhD students: P J Ker and X Zhou
    • Partners: Prof. G Buller (Heriot Watt), Prof. Joe campbell (Virginia), Dr Ian Baker (SELEX)
    • Description:
      • This proposal aims to provide IR APDs with extremely high performance, capable of detecting a single photon in the wavelength range of 1100 nm to 3000 nm. For instance they can provide low cost high performance large format imaging arrays for IR applications such as LIDAR, a technique that can provide excellent images and range measurements, non-invasive blood glucose sensing, atmospheric CO2 concentration monitoring as well as eye-safe free space optical communication. We therefore expect our APDs to generate new applications and provide highly competitive IR APDs. Based on the understanding of the InAs bandstructure, our APDs will be designed such that only electron will undergo impact ionisation to produce high avalanche gain with negligible excess noise. In addition to excellent gain, our devices can be operated at low voltage, making them compatible with off-the-shelf readout circuits. This could pave the way to a highly sensitive and affordable IR camera. To enhance the exploitation and the gain characteristics we will grow a novel InAsSb APDs on GaAs substrate which is significantly larger and cheaper than InAs substrate. This, if successful, will enable integration with commercial GaAs electronics.

A list of our previous projects

Grant title Investigators DatesFunding body
Knowledge exchange in Detectors for UV non line-of-sight communication J P R David, J S Ng, C H Tan, & P J Parbrook Nov 07 - Oct 08MoD CoI
2 Band Quantum Dot Infrared Photodiodes for Mid- and Long-Wave Infrared Scene Sensing C H Tan, J P R David, M Hopkinson, & J S Ng Nov 07 - Oct 08MoD CoI
Avalanche photodiode array detector for eye-safe 3D imaging J S Ng, C H Tan, & J P R DavidOct 07 - Sept 09 DSTL & STFC
Near infrared detectors for LIDAR J P R David & J S NgMay 06 - Sept 09 European Space Agency
Novel low voltage InAs avalanche photodiodes for affordable 2D IR detectors C H Tan, J P R David, & J S Ng Apr 06 - Mar 09 EMRS DTC
Novel low voltage InAs avalanche photodiodes for affordable 2D IR detectors (Precursor) C H Tan, J P R David, & J S Ng Oct 05 - Dec 05EMRS DTC
Secure Communications based on Quantum Cryptography J P R David & J S Ng Apr 04 - Sept 06EU FP6
High sensitivity avalanche photodiodes for imaging and rangefinding G J Rees, J P R David, and J S Ng Apr 03 - Mar 05 EMRS DTC

Updated on 16th Sept 2011 by SJD