Germanium for silicon photonics

This paper describes that Ge plays an enabler to integrate active photonic devices on a Si platform. In spite of the large lattice mismatch of ~ 4% between Ge and Si, high-quality Ge layers can be epitaxially grown on Si by ultrahigh-vacuum chemical vapor deposition. Applications of the Ge layers to near-infrared active photonic devices, i.e., photodiodes, optical modulators and light emitters, are described. Several issues on the device physics as well as the integration with Si electronics are discussed.