High Responsivity and Wide Bandwidth SiGe/Si Phototransistor for Optical Interconnection

Silicon-based hetero-junction phototransistor (HPT) is a potential optical detector promising for communication links in optic-interconnect network due to their advantages of low cost, high internal gain, high sensitivity, and compatibility with CMOS processes. In this work, a SiGe/Si HPT with double-zone base is designed and optimized to provide high responsivity and outstanding frequency characteristics simultaneously. The SiGe HPTs with different window positions and areas are fabricated using BiCMOS-compatible mesa process, and the influence of transverse parameters on HPT performance is analyzed comprehensively. With this design, a maximum optical responsivity of 8.52 A/W and a maximum optical 3 dB bandwidth of 638 MHz are demonstrated. The responsivity bandwidth product achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.69~\text {GHz}\cdot \text {A}/\text {W}$ </tex-math></inline-formula> with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50\times 50~\mu $ </tex-math></inline-formula>m2 optical window on emitter mesa under 850 nm incident light, which is expected to be applied in silicon-based optical connecting technology to simplify the optical receiving circuits and lower its power consumption.