Materials and devices.for compact optical amplification in Si photonics is reviewed. In particular, as the requirement for high gain per length together with high refractive index renders traditional oxide-based approach problematic, Er-doping of silicon-rich silicon nitride and erbium silicate nanocrystals are proposed and shown to be promising alternatives. Using such new materials, microdisk resonators and slot waveguides that concentrate the light in a compact volume for high functionality are fabricated and characterized.