High-gain bipolar phototransistor on high-resistivity silicon substrate: a new device for the detection of ionizing radiation

NPN bipolar phototransistors have been designed and fabricated on high-resistivity silicon substrates of different thicknesses, up to 800 μm. A technology featuring a double implant for the emitter allowed us to obtain a typical current gain of about 600. The device has been used to detect α particles from a ²³⁹Pu source, β particles from ⁹⁰Sr and X-rays from ²⁴¹Am using a simple experimental set-up, by directly connecting the detector to the scope. In the case of electrons, typical pulse heights of 100 mV have been observed, with pulse length of 50μs, measured on a load resistor in series to the emitter. The parameters driving the time performance have been measured, obtaining a good agreement with the electrical model of the device. We report on the functional characterization of the device with emphasis on the energy calibration and the electronic noise measurement.