Polycrystalline diamond films have been found to display p-type surface conductivity. No bulk impurity is added to the films; the p-type characteristics of the undoped diamond are thought to be due to a surface or near surface hydrogenated layer. Carrier concentrations within the range 1017–1019 cm−3 have been measured; control over the carrier concentration can be achieved by annealing the “as-grown” films in air. For a given annealing temperature a stable carrier concentration arises. The Hall carrier mobility has been explored and a value of >70 cm2/Vs has been measured for a film with a carrier concentration of ∼5×1017 cm−3, the highest reported for polycrystalline thin film diamond and equivalent to boron doped single crystal diamond.

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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.