ABSTRACT
This chapter reviews several kinds of high-speed silicon (Si)-, germanium(Ge)-, and SiGe-based high-speed photodiodes (PDs), introduces their working principles, and discusses the factors that limit their bandwidth. It introduces their applications in next-generation optical interconnect (OI) systems. Recently, several research groups have fabricated high-speed Si-based PDs on standard Si substrates by biasing these PDs under avalanche operation. The high-speed and high-gain avalanche current screens the slow diffusion current that arises from the Si substrate, leading to improvement in the bandwidth. Ge substrates can be used to fabricate high-speed Ge-based metal–semiconductor–metal (MSM) or p–i–n PDs. One of the major problems with Ge-based PDs compared with InP-based PDs is their higher dark current density. An alternative to the fabrication of high-speed Si-based PDs on the standard Si substrate is the fabrication of high-speed PDs on SOI or Ge-on-insulator (GOI) substrates, both of which show some unique advantages.
