Direct band Ge photoluminescence near 1.6 μm coupled to Ge-on-Si microdisk resonators

Abstract

We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium grown on silicon. Resonators coupled to fiber tapers display clear whispering gallery modes in transmission and photoluminescence with quality factors limited by germanium’s material absorption. Continuous wave pumping of the cavities resulted in a dominant heating effect for the cavity modes in both transmission and photoluminescence. Pulsed optical pumping proved to be more effective in minimizing heating, but was not sufficient to observe material gain or lasing. We believe that significantly higher doping levels are critical in order to achieve lasing at reasonable pump conditions.