Polycrystalline germanium enables NIR photodetectors integrated with silicon CMOS electronics

In the past two decades SiGe has been the material of choice for the realization of near infrared (NIR: 0.7-2ƒÝm) optoelectronic devices based on silicon and its technology, and several groups have developed high performance NIR photodetectors fabricated on Si substrates [ ]. Nevertheless, the existing gap between a good device and its monolithic integration with VLSI electronics on silicon had not been filled until recently, when we demonstrated the first silicon integrated circuit (IC) capable of NIR detection. [2] This was fabricated using a standard technology, but adopting a low temperature approach towards polycrystalline Ge deposition. A low thermal budget, in fact, allows monolithic integration of poly-Ge/Si heterojunction photodiodes with VLSI silicon electronics as a back-end process. After an introduction on both silicon-based NIR photodetectors and compatibility issues, we describe the novel poly-Ge deposition process and discuss the performance of poly-Ge_on_Si devices. Finally, we illustrate linear arrays of NIR detectors integrated with silicon CMOS electronics (front-end, addressing, A/D conversion and readout), demonstrating their operation and the full compatibility with standard Si CMOS technology.