Near-Infrared Sub-Bandgap All-Silicon Photodetectors: A Review

Silicon Photonics has generated an increasing interest in recent years both for optical telecommunications and for optical interconnects in microelectronic circuits. Although silicon photodiodes are excellent detectors at visible wavelengths, due to its band-gap the development of high-performance photodetectors at near infrared wavelengths has remained an imperative but unaccomplished task so far. In recent years, however, a number of near-infrared all-silicon photodetectors have been proposed and demonstrated useful in many application fields. In this paper, a review of the state of the art is presented. Devices based on mid-bandgap absorption, surface-state absorption, internal photoemission absorption and two-photon absorption are reported, their working principles elucidated and their performance discussed and compared.