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Professional and research interests have focused on semiconductor materials, in particular on the properties, physical, optical and electrical, of silicon and on various aspects of the application of silicon wafers in advanced IC and photovoltaic processes and the defect science and engineering of silicon: intrinsic point defects and their agglomerates, oxygen precipitation, gettering, dislocation dynamics and silicon mechanical properties, dielectric breakdown phenomena and minority carrier lifetime. This work has produced 70 issued patents - including the fundamental patents for so-called Perfect- and Semi-Perfect- Silicon® and Magic Denuded Zones® (MDZ®) and their variants and several important Silicon-On-Insulator (SOI) patents. Present interests include continuing work on the fundamental properties of the intrinsic point defects and nitrogen in silicon, lifetime degradation in solar cell material and advanced heterostructure designs and structures for photovoltaic and lighting applications.

• SEMI Europa Award 2001 for contribution to silicon science and technology in particular the development of PerfectSilicon and MDZ.

Semi-insulating Czochralski silicon substrates for microwave devices
D. Jordan, Dr. K. Mallik, Jian Yang, Professor R.J. Falster**, Dr. C.H. de Groot*, Professor P. Ashburn*, Dr. P.R. Wilshaw, 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, Plessey 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. 500kohm-cm in 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, ***Plessey Semiconductors.) (Funded by the EPSRC.)

Dislocation control in silicon using nitrogen implantation
Dr. J.D. Murphy, Professor R.J. Falster*, Dr. A. Jain**, 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.. (*also of MEMC Electronic Materials Inc. **Texas Instruments, USA).

The properties of nitrogen and oxygen in silicon
Dr. J.D. Murphy, Professor R.J. Falster*, 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. With support from MEMC Electronic Materials Inc.. (*also of MEMC Electronic Materials Inc.).

3 public active projects