Hot Topics
Recently Updated
- iprint with XP
Last modified: Sat Feb 6 21:58:13 GMT 2010 - iprint with Vista
Last modified: Sat Feb 6 21:56:40 GMT 2010 - Facilities
Last modified: Sat Feb 6 21:55:30 GMT 2010 - Joint Consultative Committee for Undergraduates (JCCU)
Last modified: Sat Feb 6 21:53:40 GMT 2010 - Building the cleanroom
Last modified: Sat Feb 6 21:52:22 GMT 2010
Personal Homepages
 | Dr Peter R WilshawReader in Materials |
[ Quicklinks: Research Summary Current Research Projects Recent Publications D.Phil. Projects Available ]
Summary of Research Interests
Characterisation of the electrical and mechanical properties of defects in semiconductors. The development of silicon substrates with improved properties. High resolution 2D mapping of dopant distributions in semiconductors. Development of a bioactive coating for metal implant prostheses.
Current Research Projects
Defect engineering to increase the efficiency of multi-crystalline silicon solar cells
N.J. Gregori, W.A.T. Winborn, Dr P.R. Wilshaw, Dr J.D. Murphy
Silicon solar cells account for over 90% of the solar cell market and this market is consistently growing at 40% per annum. Most of the silicon used for solar cells comes in the form of multi-crystalline wafers sliced from ingots of cast silicon. This material contains relatively high concentrations of metallic impurities, dislocations and grain boundaries, all of which enhance electron-hole recombination and hence reduce solar cell efficiency. This project aims to develop a range of novel ideas originating from the Semiconductor Group in Oxford. Ideas being developed include the use of low temperature processes to clean-up the material ("gettering") and removing defects from the material in other novel ways. The research relies on a wide range of experimental techniques, including basic electrical characterisation (IV, CV etc), electron beam induced current (EBIC), deep-level transient spectroscopy (DLTS), cathodoluminescence (CL) and possibly transmission electron microscopy (TEM). The research is performed in collaboration with leading suppliers of silicon to the photovoltaic industry, including Crystalox based in Abingdon, Oxfordshire.
Semi-insulating Czochralski silicon substrates for microwave devices
D. Jordan, Dr K. Mallik, Dr P.R. Wilshaw, Dr C.H. de Groot* , Prof P. Ashburn* , Dr R.J. Falster† , Dr K. Strickland‡ , Dr P. Osborne‡
Silicon (Si) and silicon-germanium (Si-Ge) technology has now reached a point where silicon-based group IV-IV semiconductor devices are capable of operating at frequencies up to 100 GHz, approaching the frequencies of many III-V compound semiconductor devices. However, at these frequencies standard Si substrates grown by the Czochralski (Cz) technique become very difficult to use because of the high absorption of microwave power by background free carriers present in the substrate. This results in an unacceptable degradation of the circuit performance. Thus, the performance of silicon radio frequency (RF) technology is limited to a large extent by the properties of the Si substrate used. Furthermore, this substrate-dependent restriction in the potential uses of Si will become increasingly important in coming years as even faster Si-based devices are developed. The availability of semi-insulating Cz-Si substrates would remove this limitation, and hence lead to a paradigm shift in the RF technology by extending the reach of Si-based technologies through to higher frequencies.
The aim of this project is to search for suitable deep level compensating impurities and determine the processing conditions required to produce semi-insulating handle wafers for application in RF SOI. It brings together the expertise of the University of Oxford in characterisation and diffusion of deep level impurities and that of the University of Southampton in high frequency measurements and device fabrication. The project is actively supported by close involvement of a multinational wafer manufacturer, MEMC, who will deliver the starting material and of a UK/EU RF device manufacturer, MHS Electronics, who will fabricate passive and active microwave devices on the novel high-resistivity substrates. Potentially useful initial results obtained by us include observation of resistivity ca. 10kohm-cm in Mn and Au-doped Cz-Si wafers where there has been at least a ten-fold increase in the resistivity, and effectiveness of the SiO2 diffusion barrier to Au diffusion at 1000 C. (*University of Southampton, †MEMC Electronic Materials, ‡MHS Electronics.) (Funded by the EPSRC.)
Semi-insulating Silicon
D. Jordan, Dr. R. Falster*, Dr. P.R. Wilshaw
Advanced silicon devices are working at ever higher frequencies so that an increasing number of applications which presently use III-V materials could, in principal, now use silicon. However, at these very high frequencies free carriers in the silicon substrate serve to absorb microwave energy reducing the efficiency of the circuits as a whole, so prohibiting their use. This project is to investigate a novel way to produce semi-insulating silicon substrates which would then allow the full speed of silicon devices to be utilised. In collaboration with MEMC Electronic Materials Inc. (*MEMC Electronic Materials Inc.)
Measurement and mapping of stresses in alumina with submicron resolution using cathodoluminescence in the SEM.
Dr. R.I. Todd, Dr. P.R. Wilshaw, Dr. S. Galloway*
Stress measurement in alumina and other oxides using the shift of Cr3+ fluorescence peaks is well established, and is most often accomplished by stimulating the fluorescence using laser light focused on the specimen through an optical microscope. The stress can be measured with a spatial resolution down to several micrometers by this means. The same fluorescence lines can be stimulated by incident electrons, and we are investigating the possibility of making stress measurements with submicron resolution using the Cr3+ cathodoluminescence given off by Cr-doped alumina in the electron beam of an SEM. (* Gatan Ltd.)
New Detectors for Transmission Electron Microscopy
Professor A.I. Kirkland, Dr. P.R. Wilshaw, Dr. C.J.D. Hetherington
Current generation imaging detectors for Transmission Electron Microscopy rely on a complex electron-photon conversion chain with the photons being detected by Charge Coupled Devices. As a result the overall sensitivity of these systems is poor and they are limited in their frame rate. We aim to construct the next generation of direct electron detector and this project will involve both computation and ultimately fabrication of a prototype device. (Funded by Leverhulme Trust)
Room temperature light emission from silicon
D. Stowe, K. Fraser, Dr. S. Galloway*, Dr. R. Falster**, Dr. P.R. Wilshaw
It is now known that efficient near-band-edge luminescence can be obtained from silicon provided the concentration of non-radiative recombination centres is made sufficiently small. In this project dislocations are being used as gettering centres for impurities and conditions are being optimised to produce efficient room temperature luminescence. Different annealing schedules are being developed to optimise the gettering process. (*Gatan, UK; **MEMC Electronic Materials Inc.) (With support from MEMC Electronic Materials Inc.)
An improved bone-implant interface
A. Walpole, Professor J. Triffitt*, Professor V. Baranauskas**, Dr. P.R. Wilshaw
A new coating for metal implant prostheses is being developed. This entails bonding a layer of porous alumina to the metal surface and filling the pores with a bioactive material such as bioactive glass. It is hoped that in this way the strength of the interface between the bone and implant will be improved whilst the mechanical properties of the implant are maintained. The response of human osteoblasts to porous alumina and other implant materials is being characterised. (*Nuffield Orthopaedic Centre, Oxford. **Faculdade de Engenharia Eltrica e de Computao, Universidade Estadual de Campinas, Brazil)
Secondary electron mapping of doped regions in semiconductors
Professor E. Grunbaum*, Dr. P.R. Wilshaw
The secondary electron (SE) signal in an SEM is used to produce 2-dimensional maps of doped regions in silicon and III-V semiconductors. SE images of cross-sections of doped heterostructures and laser devices reveal the type and extent of doping. Quantitative information about the observed contrast has been obtained experimentally. A model has been proposed and is being developed to account for the effect and new measurements are being made using energy filtering of the secondary electrons. (*Dept of Physical Electronics, Faculty of Engineering, Tel-Aviv University, Israel.)
Dislocation Control in Silicon using Nitrogen Implantation
C.R. Alpass, Dr R.J. Falster*, Dr A. Jain**, Dr J.D. Murphy, Dr P.R. Wilshaw
With the advent of advanced device technologies often involving heterostructures and strained layers there is an increasing problem with the generation and movement of dislocations in the near surface regions of Si wafers. This project is investigating the possibility of using ion implanted nitrogen as a high concentration source of electrically inactive nitrogen which can subsequently diffuse to and hence "lock" near surface dislocations so preventing the damaging effects that would be caused by their movement. In collaboration with Texas Instruments and MEMC Electronic Materials Inc.. (*MEMC Electronic Materials Inc. **Texas Instruments, USA).
The properties of nitrogen and oxygen in silicon
C.R. Alpass, Dr R.J. Falster*, Dr J.D. Murphy, Dr P.R. Wilshaw
Nitrogen doped silicon is an attractive candidate for improved substrates for the next generation of high-performance electronic devices. As well as pinning dislocations (hence increasing wafer strength) and reducing the formation of void regions, nitrogen is known to affect oxygen precipitation. Since device manufacturers use oxygen precipitates in "internal gettering" processes to trap harmful impurities (such as iron, copper and nickel) in regions of the material in which they are least detrimental to device performance, the addition of nitrogen provides them with more flexibility in these gettering processes. Despite its undoubted promise for improved wafer performance, the properties of nitrogen in silicon are still largely unknown. This project will aim to further the understanding of nitrogen in silicon, and its interaction with oxygen, using a novel dislocation locking technique developed in Oxford over the past few years. The mechanism of nitrogen transport will be studied, elucidating the species responsible and the role of oxygen, together with parameters that describe its interaction with dislocations and hence the mechanical strength of wafers. Electrical measurements (DLTS, PL, FTIR) will be made to characterise the activity of the different species involved. It is anticipated that the information gained will be of direct and immediate relevance to the semiconductor industry hence the work will be carried out in close collaboration with wafer manufacturers (MEMC Electronic Materials, Siltronic and Topsil) and other UK universities. With support from MEMC Electronic Materials Inc.. (*MEMC Electronic Materials Inc.).
Optically induced degradation of Czochralski silicon solar cells
C.R. Alpass, Dr R.J. Falster*, Dr J.D. Murphy, Dr P.R. Wilshaw
The efficiency of Czochralski silicon solar cells degrades significantly on exposure to sunlight. In this project the influence of light on oxygen diffusion in silicon at low temperatures is being investigated. The purpose is to determine whether electron hole pairs generated by the illumination are responsible for enhanced oxygen diffusion. In collaboration with MEMC Electronic Materials Inc.. (*MEMC Electronic Materials Inc.).
Determination of grain boundary orientation in multi-crystalline silicon by photon reflection
Dr P.R. Wilshaw, Dr J.D. Murphy, Dr A.J. Wilkinson
Silicon solar cells account for over 90% of the solar cell market and this market is consistently growing at 40% per annum. Most of the silicon used for solar cells comes in the form of multi-crystalline wafers, in which the grains are typically 1 to 20mm across. Wafer manufacturers are in urgent need of a low-cost technique which allows them quickly to identify the orientations of the grains. The project involves developing such a technique by analysing the patterns produced when a laser beam reflects from the wafer surface. The pattern analysis is expected to be similar to that carried out in electron backscattered diffraction (EBSD). The project is in collaboration with Dr S. Senkader of ScanWafer, Norway.
Exploring Electrophen™ polymer as a semiconductor device material
C. Alpass, Dr K. Mallik, Dr P.R. Wilshaw, Dr A. Crossley, Dr J. Doyle*, Mr M. Stannard*, Dr G. Murray*
Electrophen™ has been proved to be a high quality material for making bipolar plates in polymer electrolyte membrane fuel cells. The material has further potentials. In this project Electrophen™ is being explored as a semiconductor device material. The study focuses on electrical and optical properties of this new material as a function of its growth compositions and processing.(*Bac2 Limited) (Funded by Bac2 Limited.)
13 public active projects
Research Publications
Wilshaw, P.R., Mallik, K. and Falster, R.J. (2006). 'Substrate for High Frequency Integrated Circuits UK Patent 0618202.6 15th Sept 2006'.
Mallik, K., de Groot, C.H., Ashburn, P. and Wilshaw, P.R. (2006). 'Enhancement of resistivity of Czochralski silicon by deep level manganese doping' Applied Physics Letters 89(11).
Breese, M.B.H., Huang, L., Teo, E.J., King, P.J.C. and Wilshaw, P.R. (2005). 'Transmission ion channeling analysis of isolated 60 degrees misfit dislocations' Applied Physics Letters 87(21).
Stowe, D.J., Fraser, K.J., Galloway, S.A., Senkader, S., Falster, R.J. and Wilshaw, P.R. (2005). 'Efficient, room-temperature, near-band gap luminescence by gettering in ion implanted silicon'. "Microscopy of Semiconducting Materials". Cullis, A.G.,Hutchison, J.L. 107 355-358.
Murphy, J.D., Giannattasio, A., Alpass, C.R., Senkader, S., Falster, R.J. and Wilshaw, P.R. (2005). 'The influence of nitrogen on dislocation locking in float-zone silicon'. "Gettering and Defect Engineering in Semiconductor Technology Xi". 108-109 139-144.
Evans-Freeman, J.H., Emiroglu, D., Vernon-Parry, K.D., Murphy, J.D. and Wilshaw, P.R. (2005). 'High resolution deep level transient spectroscopy applied to extended defects in silicon' Journal of Physics-Condensed Matter 17(22) S2219-S2227.
Giannattasio, A., Murphy, J.D., Senkader, S., Falster, R.J. and Wilshaw, P.R.: 'Oxygen and nitrogen transport in silicon investigated by dislocation locking experiments' Journal Of The Electrochemical Society 152 (6) (2005) G460-G467.
Giannattasio, A., Murphy, J.D., Senkader, S., Falster, R.J. and Wilshaw, P.R.: 'Oxygen and nitrogen transport in silicon investigated by dislocation locking experiments (vol 152, pg G460, 2005)' Journal Of The Electrochemical Society 152 (8) (2005) L12-L12.
Murphy, J.D., Giannattasio, A., Senkader, S., Falster, R.J. and Wilshaw, P.R.: 'Nitrogen transport in float-zone and Czochralski silicon investigated by dislocation locking experiments' Physica Status Solidi A-Applications And Materials Science 202 (5) (2005) 926-930.
Senkader, S., Giannattasio, A., Falster, R.J. and Wilshaw, P.R.: (2004). 'Dislocation locking in silicon by oxygen and oxygen transport at low temperatures'. Gettering And Defect Engineering In Semiconductor Technology. 95-96: 43-52.
Barkay, Z., Grunbaum, E., Shapira, Y., Wilshaw, P., Barnham, K., Bushnell, B., Ekins-Daukes, N.J. and Mazzer, M. (2004). High-resolution scanning electron microscopy of dopants in p-i- n junctions with quantum wells. Electron Microscopy And Analysis 2003: 143-146.
Briggs, E.P.K., M., Walpole, A.R., Palsgard, E. and Wilshaw, P.R.: 'Formation of highly adherent nano-porous alumina on Ti-based substrates: a novel bone implant coating.' Journal Of Materials Science: Materials in Medicine 15 (2004) 1-9.
Giannattasio, A., Senkader, S., Falster, R.J. and Wilshaw, P.R.: 'The role of prismatic dislocation loops in the generation of glide dislocations in Cz-silicon.' Computational Materials Science 30 (1-2) (2004) 131-136.
Mallik, K., Falster, R.J. and Wilshaw, P.R.: 'Schottky diode back contacts for high frequency capacitance studies on semiconductors.' Solid-State Electronics 48 (2) (2004) 231-238.
Giannattasio, A., Murphy, J.D., Senkader, S., Falster, R.J. and Wilshaw, P.R. (2004). Impurity Locking of Dislocations in Silicon. Electrochemical Society Proceedings "High Purity Silicon": 39-54.
Booth S.E., Marsh C.D., Mallik K., Baranauskas V., Sykes J.M. and Wilshaw P.R.: 'Fabrication of nanocrystalline aluminium islands using double- surface anodization' Journal of Vacuum Science & Technology B 21, 316-318 (2003).
Giannattasio A., Senkader S., Azam S., Falster R.J. and Wilshaw P.R.: 'The use of numerical simulation to predict the unlocking stress of dislocations in Cz-silicon wafers' Microelectronic Engineering 70, 125 (2003).
Karlsson M., Palsgard E., Wilshaw P.R. and Di Silvio L.: 'Initial in vitro interaction of osteoblasts with nano-porous alumina' Biomaterials 24, 3039-3046 (2003).
Mallik K., Falster R.J. and Wilshaw P.R.: ''Semi-insulating' silicon using deep level impurity doping: problems and potential' Semiconductor Science and Technology 18, 517-524 (2003).
Senkader S., Giannattasio A., Falster R.J. and Wilshaw P.R.: 'On the dislocation-oxygen interactions in Czochralski-grown Si: oxygen diffusion and binding at low temperatures' Journal of Physics-Condensed Matter 14, 13141-13145 (2002).
Senkader S., Giannattasio A., Falster R.J. and Wilshaw P.R.: 'Dislocation locking in silicon by oxygen and oxygen transport at low temperatures' Solid State Phenomena 95/96, 43-52 (2003).
Giannattasio, A., Senkader, S., Falster, R.J. and Wilshaw, P.R.: 'Dislocation locking by nitrogen impurities in FZ-silicon.' Physica B-Condensed Matter 340 (2003) 996-1000.
Stowe, D.J., Galloway, S.A., Senkader, S., Mallik, K., Falster, R.J. and Wilshaw, P.R.: 'Near-band gap luminescence at room temperature from dislocations in silicon.' Physica B-Condensed Matter 340 (2003) 710-713.
Stowe, D.J., Galloway, S.A., Senkader, S., Mallik, K., Falster, R.J. and Wilshaw, P.R. (2004). A room temperature cathodoluminescence study of dislocations in silicon. Electron Microscopy And Analysis 2003: 67-70.
Walpole, A.R., Briggs, E.P., Karlsson, M., Palsgard, E. and Wilshaw, P.R.: 'Nano-porous alumina coatings for improved bone implant interfaces.' Materialwissenschaft Und Werkstofftechnik 34 (12) (2003) 1064-1068.
Giannattasio A., Senkader S., Falster R.J. and Wilshaw P.R.: 'Generation of dislocation glide loops in Czochralski silicon' Journal of Physics-Condensed Matter 14, 12981-12987 (2002).
Projects Available
Production of Semi-Insulating Silicon for High Frequency Devices
P R Wilshaw / Kanad Mallik
This project will provide an opportunity to research the making of semi-insulating (resistivity of 10-100kohm-cm) silicon-on-insulator (SOI) substrates grown by the Czochralski technique for microwave monolithic integrated circuits (MMIC). This has been identified as a novel substrate material in the ITRS Roadmap and has the potential to bring about a paradigm shift in the semiconductor industry.
The research involves enhancement of the resistivity of SOI handle wafers by doping with transition elements, which introduce deep impurity levels in the silicon energy band gap. Another challenging aspect of the research is to confine these dopants to the handle wafer by use of diffusion barriers. The work will provide an excellent opportunity to get training and gain experience in a wide range of experimental skills in modern semiconductor science and technology. For example:
- Transition element doping techniques, including ion implantation and diffusion.
- Characterization techniques like, deep level transient spectroscopy (DLTS), secondary ion mass spectroscopy (SIMS), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and microwave absorption measurements.
- Some of the characterisation experiments will involve training in high vacuum techniques and cryogenics.
- Semiconductor device fabrication using photolithography.
- Working in semiconductor-grade cleanrooms in Southampton and Oxford.
- There is also scope for numerical modelling work concerning the electronic properties of semiconductors and microwave device simulation.
The student will work in a team involving members of the Department of Materials, Oxford, the Electronic Engineering Department, Southampton, a multi-national Si wafer manufacturer, and a UK/EU semiconductor device manufacturer.
Also see homepages:Kanad Mallik Peter Wilshaw
Defect engineering to increase the efficiency of multi-crystalline silicon solar cells
J D Murphy / P R Wilshaw
Silicon solar cells account for over 90% of the solar cell market and this market is consistently growing at 40% per annum. Most of the silicon used for solar cells comes in the form of multi-crystalline wafers sliced from ingots of cast silicon. This material contains relatively high concentrations of metallic impurities, dislocations and grain boundaries, all of which enhance electron-hole recombination and hence reduce solar cell efficiency. This project aims to develop a range of novel ideas originating from the Semiconductor Group in Oxford. Ideas to be developed include the use of low temperature processes to clean-up the material ("gettering") and removing defects from the material in other novel ways. The research will rely on a wide range of experimental techniques, including basic electrical characterisation (IV, CV etc), electron beam induced current (EBIC), deep-level transient spectroscopy (DLTS), quasi-steady-state photoconductance decay (QSS-PCD), cathodoluminescence (CL) and possibly transmission electron microscopy (TEM). The research will be performed in lose collaboration with leading suppliers of silicon to the photovoltaic industry.
Also see homepages:John Murphy Peter Wilshaw
The properties of nitrogen and oxygen in silicon
J D Murphy /P R Wilshaw
Nitrogen doped silicon is an attractive candidate for improved substrates for the next generation of high-performance electronic devices. As well as pinning dislocations (hence increasing wafer strength) and reducing the formation of void regions, nitrogen is known to affect oxygen precipitation. Since device manufacturers use oxygen precipitates in "internal gettering" processes to trap harmful impurities (such as iron, copper and nickel) in regions of the material in which they are least detrimental to device performance, the addition of nitrogen provides them with more flexibility in these gettering processes. Despite its undoubted promise for improved wafer performance, the properties of nitrogen in silicon are still largely unknown. This project will aim to further the understanding of nitrogen in silicon, and its interaction with oxygen, using a novel dislocation locking technique developed in Oxford over the past few years. The mechanism of nitrogen transport will be studied, elucidating the species responsible and the role of oxygen, together with parameters that describe its interaction with dislocations and hence the mechanical strength of wafers. Electrical measurements (DLTS, PL, FTIR) will be made to characterise the activity of the different species involved. It is anticipated that the information gained will be of direct and immediate relevance to the semiconductor industry hence the work will be carried out in close collaboration with wafer manufacturers (MEMC Electronic Materials, Siltronic and Topsil) and other UK universities.
Also see homepages:John Murphy Peter Wilshaw
New detectors for transmission electron microscopy
A Kirkland / P R Wilshaw / G. Moldovan
Current generation imaging detectors for Transmission Electron Microscopy rely on a complex electron-photon conversion chain with the photons being detected by Charge Coupled Devices. As a result the overall sensitivity of these systems is poor and they are limited in their frame rate. We aim to construct the next generation of direct electron detector and this project will involve both simulation and fabrication of prototype devices.
Also see homepages:Angus Kirkland Peter Wilshaw
Also see a full listing of New projects available within the Department of Materials.
