Distributed Bragg reflectors integration in highly strained Ge micro-bridges on 200 mm GeOI substrates for laser applications

Highly strained germanium is thought of as a gain medium for silicon photonics laser sources. In order, to turn the bandgap from indirect to direct, tensile strain is nowadays investigated. This could lead in the future to the monolithic integration of efficient germanium-based laser sources with Si microelectronics technologies. Recent results show that several percent of strain can be induced in Ge micro-bridges [1-2]. The other key parameter to build a laser is definition of a cavity. Whispering gallery mode [3] or short cavities like VCSEL or photonic crystals [4-5] were proposed in the literature. Here, we present long and strained cavities that were obtained through the use of Distributed Bragg Reflectors (DBR) on each side of suspended Ge micro-bridges. Devices are fabricated from high quality 200 mm Germanium-On-lnsulator (GeOI) substrates obtained by the Smart-Cut™ technology. Such substrates are used to enhance the rapture strain limit of the germanium bridges thanks to the lack of dislocations at interfaces. Laser design modelling, membrane processing and experimental results will be presented in detail.