1. Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
2. Cambridge CMOS Sensors Ltd., Deanland House, 160 Cowley Road, Cambridge CB4 0DL, United Kingdom
3. Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
4. School of Engineering, University of Warwick, Coventry CV4 7AL, United Kingdom