Photodetectors with CVD diamond films: Electrical and photoelectrical properties photoconductive and photodiode structures

Abstract

Free-standing and silicon-supported diamond films have been used to fabricate photoconductive and photodiode structures for UV light detection. Planar and sandwiched photoconductive structures have been made on microwave plasma-grown free-standing CVD polycrystalline diamond films of 200 μm and 15 μm thicknesses, respectively. A photodiode sandwich structure was obtained on thin (≈2 μm) boron-doped diamond films grown on silicon substrate by hot filament CVD. Parameters of defects in the structures were studied by charge-based deep-level transient spectroscopy (Q-DLTS). Planar photoconductive detectors after annealing in air showed a low dark current < 10 pA and a high spectral discrimination-a 104 higher response to 200 nm than to visible (600 nm) wavelengths. The dark current was < 10 pA. The turn-off time of the device following exposure to light was less then 10 ms. It was found that the annealing in air decreases density of point defects more than order and strongly increases wavelength discrimination. The sandwich photodiodes showed a sharp cut-off in photoresponse at 220 nm with a quantum yield of about 0.3 and a photovoltage in the open circuit regime of up to 1.6 V. Such photodiodes can be used not only for light detection but also for light energy transformation into electrical energy as in a photovoltaic cell.