Considerable interest exists in fabrication of electronic devices from thin film polycrystalline diamond. To date, doping this material to achieve good free carrier concentrations and mobilities at room temperature has proved difficult. In this letter we report low temperature Hall effect measurements made on diamond films subjected to a hydrogenation process, such that the near surface region becomes p type without the addition of conventional dopant atoms. High carrier concentrations and mobilities can be achieved. The change in carrier concentration within the temperature range 10–300 K does not change as expected for most films, actually increasing as the temperature falls. This effect could be related to the confinement of carriers at the surface caused by the dipole provoked by adsorbed hydrogen on the diamond. However, polished films display more conventional behavior in that the carrier concentration falls with falling temperature.

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A photodiode has been constructed from lightly boron doped, Si supported, thin film chemically vapor deposited (CVD) diamond which shows over five orders of magnitude discrimination between deep UV (≤220 nm) and visible light. A thin (10 nm) gold Schottky barrier with an associated Ti–Ag–Au ohmic contact was used to create a rectifying device with low (≤2 pA) dark currents when reversed biased. This structure showed a sharp cut off in photoresponse at 220 nm, the band gap energy of diamond. Conversely, a photoconductive device fabricated from similar (nominally undoped) material gave a broader UV photoresponse and displayed high dark currents; the superior performance of the diode structure on fine grain material is discussed.

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A metal–semiconductor–metal Schottky barrier photodetector has been fabricated on a “hydrogen-doped” surface-conducting chemical vapor deposition (CVD) diamond. The device is fabricated in one step by forming two back-to-back aluminum Schottky diodes on the p-type surface. This simple process is compatible with previously reported metal–semiconductor field-effect transistor fabrication on this type of CVD diamond and offers the prospect of the monolithic integration of a ultraviolet detector and active circuitry. Preliminary electrical and optical characteristics of the device have been measured, including the spectral response over the range 180–800 nm. The device exhibits a linear response with the applied optical power at 220 nm, operates at a bias of only 2 V, and shows visible blind characteristics, with a spectral discrimination of three orders of magnitude as determined from the ratio of 200–550 nm responses.

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