Germanium light sources for silicon photonics

Germanium (Ge) is a group-IV semiconductor promissing for both advanced electronics and photonics applications integrated on Silicon (Si) chips. The high electron mobility is favourable for the Complementary Metal-Oxide-Semiconductor (CMOS) transistors, while the quasi-indirect band gap character is useful for developing light sources for Si photonics. In this talk, we will review the current developments of Ge light sources fabricated using nano-fabrication technologies compatible with CMOS processes. In particular, we review recent progress in applying high-tensile strain to Ge to reduce the direct band gap. By making a freestanding beam using Micro-Electro-Mechanical-Systems (MEMS) processes, extremely high-tensile strain exceeding a few % can be applicable to Ge, converting indirect to direct band gap characters. Another important process is doping Ge with donor impurities to fill the indirect band gap valleys in the conduction band. Realization of carrier confinement structures and suitable optical cavities will also be discussed. Finally, we will discuss various applications of Ge light sources in potential photonics-electronics convergent systems