Persistent photocurrents in CVD diamond
Persistent photocurrents (PPCs) in undoped polycrystalline CVD diamond are generated by UV illumination with 5.5 eV photons. PPCs are several orders of magnitude larger than dark currents and can be annealed at T > 550 K. The PPC annealing dynamic is stretched exponentially with an activation energy of 1.4 eV. Thermally stimulated currents (TSCs) are dominated by maxima around 550 K which are related to a trap level 1.4 eV deep in the energy gap of CVD diamond. UV illumination generates a photocurrent response with an onset at hv > 0.6 eV measured by spectrally resolved photocurrents. A model is discussed which accounts for the detected phenomena where electrons are captured in grain boundaries and holes in defects in the grains of CVD diamond.