We demonstrate the combination of germanium microdisks tensily strained by silicon nitride
layers and circular Bragg reflectors. The microdisks with suspended lateral Bragg reflectors
form a cavity with quality factors up to 2000 around 2 μm. This represents a key feature to
achieve a microlaser with a quasi-direct band gap germanium under a 1.6% biaxial tensile
strain. We show that lowering the temperature significantly improves the quality factor of the
quasi-radial modes. Linewidth narrowing is observed in a range of weak continuous wave …