A high voltage computer controlled experimental system for the investigation of amorphous semiconductors as image sensors

Abstract

This paper describes an ongoing programme of work designed to investigate dark discharge and photoconductivity in amorphous semiconductors with a view to applying these materials to industrial optical process tomography (OPT). Extensive laboratory equipment has been developed to investigate the aforementioned phenomena in amorphous arsenic triselenide (a-As₂Se₃) and hydrogenated amorphous silicon (a-Si: H). Photoconductivity measurements are performed in both xerographic and electroded modes by the use of a purpose built xenon ‘ash facility which can deliver pulsed light of user defined intensity, duration, and frequency. Control of the laboratory apparatus and the collection of data is fully automated, and the laboratory apparatus conforms to all relevant health and safety regulations concerning working with high voltages. Extensive software has been written for the data handling, data management, data display and numerical analysis of the experimental data. The advantages of amorphous semiconductors for OPT are discussed in section 1. Section 2 contains an overview of the developed experimental apparatus, and finally, section 3 brie‘y describes the amorphous semiconductor material’s ability to produce qualitative and quantitative data for imaging or control signal generation.

Keywords

amorphous experimental apparatus image sensors process tomography semiconductor

References

Apte, R. B. , Street, R. A. , Ready, S. E. , Jared, D. A. and Moore, A. M. 1998: Large area, low noise amorphous silicon imaging system. In Blouke, Morley M. , editor, Solid state sensor arrays. Development and applications II. Society of Photo-optical Instrumentation Engineers, 3301, 2-8.

Bauer, G. H. and Paasche, S. M. 1987: Amorphous Si/SiC three layer structures for xerographic applications. Journal of Applied Physics 62, 268-268.

Baxendale, M. 1989: Xerographic spectroscopy and depletion discharge studies of a-Se, a-Se: Te alloy, a-As₂Se₃, and a-Si: H photo-receptors. PhD thesis, Imperial College, London.

Borsenburger, P. M. and Wiess, D. S. 1993: Organic photoreceptors for imaging. New York: Marcel Decker, 4-4.

Borsenburger, P. M. and Wiess, D. S. 1998: Organic photoreceptors for xerography. New York: Marcel Decker, 40-40.

Chan Y.C. 1983: Xerographic properties of CdS and ZnO semiconductor powder resin binder layers. PhD thesis, Imperial College, London.

Cobine T. D. 1958: Gaseous conductors. New York: Dover, 254-255.

Elliot, S. R. 1992: Physics of amorphous solids. London: Longman.

Fletcher, M. J. 1996: A review of optical inspection methods. INSIGHT 38, 270-270.

10.

Jenner, R. P. and Vaezi-Nejad, S. M. 1998: Development of instrumentation for a novel computer controlled experimental apparatus. Proceedings of the Second International Conference on Planned Maintenance, Reliability, and Control, University of Oxford, 109-109.

11.

Jenner, R. P. and Vaezi-Nejad, S. M. 1999: Development of a novel light source for the investigation of optical sensors. Measurement and Control 32, 75-78.

12.

Joshi, N. V. 1990: Photoconductivity: art, science, and technology. New York: Marcel Dekker.

13.

Kasap, S. O. 1991: Photoreceptors: the selenium alloys. In Diamond, A. S. , editor, Handbook of imaging materials. New York: Marcel Decker, 329-329.

14.

Kaura, T. and Srivastava, V. K. 1987: Surface potential decay in stretched and unstretched PVDF films. Journal of Electrostatics 15, 46-46.

15.

Keithley Instruments Inc. 1984: Low current measurements, Application note #100.

16.

Mort, J. 1991: Applications of amorphous silicon and related materials in electronic imaging. In Diamond, A. S. , editor, Handbook of imaging materials. New York: Marcel Decker, 448-448.

17.

Mott, N. F. and Davis, E. A. 1979: Electronic processes in non-crystalline materials, second edition. Oxford: Clarendon Press.

18.

Neitzel, U. , Maack, I. and Günther-Kohfahl, S. 1994: Image quality of a digital chest radiography system based on a selenium detector. Medical Physics 21, 509-516.

19.

Pai, D. M. 1997: Time of ‘ight study of the compensation mechanism in a-Se alloys. Journal of Imaging Science and Technology 41, 135-135.

20.

Pisarkiewicz, T. and Kuta, S. 1997: A measurement set-up for photoconductivity decay experiments. Measurement Science and Technology 9, 1007-1009.

21.

Schaffert, R. M. 1975: Electrophotography. London: Focal Press, 397-397.

22.

Stark, W. 1995: Surface potential homogeneity of corona charged FEP and PVDF electrets. Journal of Electrostatics 25, 277-285.

23.

Vaezi-Nejad, S. M. and Jenner, R. P. 1997: Principles and applications of advanced transient photoconductivity techniques. Proceedings of the IEEE Instrument and Measurement Technology Conference, Ottawa, Canada, Vol. 2, 942-942.

24.

Williams, R. A. and Beck, M. S. 1995: Process tomography principles, techniques and applications. Oxford: Butterworth-Heinemann, 5-6.