Lansley, Stuart Peter; (2002) Diamond Photodetectors for Deep Ultra-Violet Applications. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Diamond has many extreme properties, both physical and electronic. With an electronic bandgap of 5.5eV semiconducting diamond is an attractive candidate for photodetectors working in the deep ultra-violet region; the bandgap corresponding to an intrinsic long- wavelength threshold around 225nm. In the absence of any extrinsic absorption, visible-blind photodetectors may be realised. The physical, chemical and radiation hardness of diamond could allow such devices to be used in harsh environments where the conditions damage, and degrade the performance of, devices fabricated on more traditional semiconductor materials. Traditionally, the variability and rarity of natural diamond stones have made cost a prohibitive factor in the use of diamond as an electronic material. However, the development of synthetic fabrication techniques, such as chemical vapour deposition (CVD), has enabled the production of lower cost diamond, but with properties approaching the ideal properties of diamond. This thesis describes the use of CVD diamond for the realisation of deep ultra-violet photodetectors. The electrical, spectral and temporal characteristics of diamond photoconductors are examined. A two-stage methane/air heat treatment is used to passivate defects in the CVD diamond and hence improve the device characteristics. Ultra-violet photodetectors have uses in various fields; one of the most recent of which has arisen from the plan to use deep ultra-violet light during the photolithography stage of semiconductor chip manufacture. Detectors will be required for beam monitoring and profiling. Excimer laser wavelengths of 193nm (ArF) and then 157nm (F2) have been chosen by Sematech as future wavelengths to be used. At these wavelengths silicon detectors are inefficient, as well as being sensitive to visible wavelengths, and are easily damaged. The intrinsic absorption of diamond at these wavelengths, along with its radiation hardness, make diamond a suitable material for such detectors. Pulses from both ArF and F2 excimer lasers have been detected and are analysed here. Also reported is the first demonstration of an optically modulated field effect transistor (OPFET) fabricated on diamond. The device utilises the "doping"-effect of the hydrogen-terminated surface of CVD diamond.

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