Germanium lasers may help photonic integration with silicon

摘要

Germanium could be the key ingredient needed to integrate high-speed optical interconnects with silicon integrated-circuit chips and two independent groups have taken important steps toward germanium-on-silicon structures. Researchers at the Massachusetts Institute of Technology (Cambridge, MA) have grown germanium photodetectors on silicon and are developing germanium lasers. Last month at the International Electron Devices Meeting (IEDM; Washington, D.C.), CheeWee Liu of National Taiwan University (Taipei, Taiwan) reported room-temperature operation of an electronically pumped germanium laser, although it was not on silicon. Silicon makes excellent integrated elecsilicon layers. For a 120-(mu)m-long germanium laser, the group calculates threshold current density of 5.8 kA/cm~(2), compared to 1 kA/cm~(2) for a typical III-V layer. So far, the group has demonstrated modulation depth of 5 dB, but expects to improve that. "We think we can get to 10 dB without any problem," Michel says, adequate for optical interconnects. The group expects bandwidth to exceed 40 GHz.