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Details of Grant 

EPSRC Reference: GR/H39581/01
Principal Investigator: Amaratunga, Professor G
Other Investigators:
Milne, Professor WI
Researcher Co-Investigators:
Project Partners:
Department: Engineering
Organisation: University of Cambridge
Scheme: Standard Research (Pre-FEC)
Starts: 01 July 1992 Ends: 30 September 1995 Value (£): 87,793
EPSRC Research Topic Classifications:
Materials Synthesis & Growth
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:  
Summary on Grant Application Form
To investigate the electronic properties amorphous diamond-like carbon deposited at low temperatures and its use in electronic devices.Progress:The project is concerned with the use of diamond-like carbon (DLC) films as an amorphous semiconductor in electronic devices. The research undertaken thus far has involved two distinct forms of DLC. One which is deposited in thin film form starting from a hydrocarbon gas, CH4, which is excited using capacitive rf system to form a plasma. The other type of DLC is obtained by running an electric arc on a graphite cathode in vacuum, and condensing the resulting vapour (plasma) to obtain a thin film. The major difference in the films obtained is that the former contains hydrogen (due to the use of a hydrocarbon gas source) while the latter allows for a hydrogen free carbon film. It is now well established that carbon films formed without hydrogen from a vacuum arc plasma can have up to 80% sp3 diamond-like bonding and is the closest material to an amorphous diamond - more accurately termed tetrahedral amorphous carbon (ta-C). However, both types of DLC have a higher amount of residual defect states in the band-gap which limits their use as an electronic material. A large part of the research has been carried out to date has been focused on evaluating the electronic density of states in DLC and how the defect density can be reduced. The vacuum arc deposited ta-C has proven to be a hopeful material with demonstration of electronic doping and some photoconductivity. However, as an electronic material its characteristics are still far inferior to those of a-Si:H. However, very recent results obtained from our rf plasma DLD films deposited from CH4/Ar/N2 gas plasma under magnetic confinement have been very encouraging. We are now actively pursuing nitorgenated DLC, a-C:H:N and a-C:N, as a possible route to obtaining a carbon based amorphous semiconductor. In parallel with material investigation, device development has also been undertaken. Two of the areas explored to date have been the use of DLC as a wide-bandgap emitter for Si HBTs and as thin-film transistor material for displays. Devices fabricated to date have shown a bipolar gain close to 1. We believe that this is limited by recombination at the DLC/Si interface and that with careful processing this can be dramatically improved. Thin film transistor development has now reached the stage where a suitable gate dielectric using plasma deposited SiNx has been developed. One of the issues which is being addressed at present is the removal of the 'graphite like' surface layer which exists on DLC films. The most innovative device related results obtained to date are related the fabrication DLC superlattices. We had shown prior to the commencement of the projects that the optical band-gap of DLC could be varied in the range 1.2-4 eV. We have successfully used this property of DLC to make all carbon amorphous superlattice structures and demonstrated that quantum size effects and resonant tunnelling can be obtained[1]. Device applications of such DLC superlattice structures are now under consideration.[1] S.R.P. Silva, G.A.J. Amaratunga, C.N. Woodburn, M.E. Welland and S. Haq, Quantum size effects in amorphous diamond-like carbon superlattices , Japanese Journal of Applied Physics, 33, p.6458 (1994).
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Organisation Website: http://www.cam.ac.uk