Finger emitter/base bipolar junction phototransistors for optical gas sensing in the blue spectral region

In this work we report on the design, fabrication, electrical characterization and sensing tests of new silicon bipolar junction phototransistors, coated by Zn-(heptiloxy)-TPP. The finger-shaped emitter/base junction has been proved to enhance the responsivity in the blue spectral region with respect to the standard fully implanted detector (0.24A/W and 0.14A/W respectively at 5 V reverse bias). This effect has been experimentally tested in reverse biased E/B junction and, even though the phototransistor is operated with floating base, slightly forward biasing the E/B junction, this improvement in responsivity was still observed. The new transducers exhibit a beta current gain higher than 150 and were employed to detect ethanol concentrations down to 300ppm.