Substrate resistivity influence on silicon–germanium phototransistor performance

This Letter presents the impact of silicon substrate resistivity on SiGe phototransistors. SiGe phototransistors were fabricated on the commercially available SiGe/Si bipolar technology. The performances of the phototransistors fabricated based on low‐ and the high‐resistive silicon substrate are compared. The phototransistor based on low‐resistivity (LR) silicon substrate provides a responsivity of more than double compared to the phototransistor based on a high‐resistivity silicon substrate that is fabricated by using the same bipolar transistor technology. The phototransistor fabricated on LR substrate exhibits low‐frequency responsivity up to 1.35 A/W (at 50 MHz).