Photocurrent amplification by gate effect in a three terminal carbon nanotube /n-Si photodetector. Display omitted •Three terminal Carbon Nanotube/n-Si photodetectors.•Time response to nanosecond laser pulse.•Collecting photocharges by interdigitated electrodes.•Voltage doping in carbon nanotube/n-Si photodetectors. We investigated the response of carbon nanotube/Si photodetectors to nanosecond light pulse using two electrode configurations for photovoltaic and photoconductive operations. When operating in photovoltaic mode, the devices show a linear dependence of the photocurrent as a function of the light pulse energy with rise time of 20 ns. In photoconductive mode, an increase of the maximum photocurrent as high as 30 times and a gain in the number of photogenerated charges up to 200% is recorded with a correspondent decrease in the time response below 10 ns. Current voltage characteristics measured as a function of the temperature indicate that the fast response of these devices can be ascribed to the formation of Schottky junctions at carbon nanotube/Si interface. These results make our devices comparable to most commercial photodetectors and pave the way for their use as avalanche photomultipliers.