Enhanced light emission from Ge dots in optical microcavities

Abstract

The light emission from Ge quantum dots are in the range of 1.3 to 1.6 µm which is the telecommunication wavelengths. Light-emitting devices based on Ge quantum dots embedded in optical microcavities are one possible solution for Si light source. In order to enhance the light emission, we embed Ge self-assembled quantum dots into various Si microcavities. Due to the Purcell effect, the light emission intensity is greatly enhanced by the by the optical resonance in the cavity. Site-controlled array of single Ge quantum dots are grown on patterned silicon-on-insulator substrate. Single Ge dots are then precisely embedded into photonic crystal microcavities. Resonant photoluminescence in telecom band was observed from single Ge dot at room-temperature. Strong enhancement of PL intensity is observed from GeSi SQD coupled to modified L3 type PhC cavity. The strongest resonant luminescence peak is obtained at 1.5 µm nm, with an enhancement factor over three orders. A Purcell factor over 60 is estimated from the PL enhancement. We attribute the accurate spatial and spectral overlap between SQD and PhC cavity to be the main reason for the high Purcell factor. The PL results also implying that two-level system is not proper to describe the band structure of large size GeSi SQD. The dot ordering and alignment provides a scalable, low cost method to fabricate Si-based single quantum dot-cavity systems.