State-of-the-art all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths

• Published in: Laser & photonics reviews 2016-11, Vol.10 (6), p.895-921
• Main Authors: Casalino, Maurizio, Coppola, Giuseppe, De La Rue, Richard M., Logan, Dylan F.
• Format: Article
• Language: English
• Subjects: Absorption; Devices; graphene; infrared; optical microcavity; photodetector; Photodetectors; Photonics; Silicon; State of the art; Telecommunications; Wavelengths
• ISSN: 1863-8880; 1863-8899
• DOI: 10.1002/lpor.201600065

Silicon‐based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics. In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption ‐ due to its bandgap of 1.12 eV. Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 1.1 μm, in recent years tremendous advances have been made in the field of all‐silicon sub‐bandgap photodetectors at telecom and datacom wavelengths. By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well‐established technologies, and are opening new and intriguing perspectives. In this paper, a review of the state‐of‐the‐art is presented. Devices based on defect‐mediated absorption, two‐photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared. This review focuses on sub‐bandgap all‐silicon photodetectors operating at telecom and datacom wavelengths. After a short introduction to the theory of the main photo‐conversion mechanisms allowing detection at sub‐bandgap wavelengths in silicon, an overview of the more recent all‐silicon photodetectors based on both innovative structures and emerging materials, will be presented, discussed and compared. The review also helps identifying future developments necessary to compare favourably with devices based on III‐V elements.