An efficient electrically injected group-IV light source compatible with the complementary metal-oxide-semiconductor (CMOS) process is the holy grail for realizing functional, intelligent electronic-photonic integrated circuits for a wide range of applications. The group-IV GeSn material is considered as a promising solution for efficient light sources because its bandgap can be fundamentally transformed from indirect to direct with appropriate Sn compositions. However, an important challenge in realizing efficient electrically injected light emitters is the incorporation of an optical cavity with electrical structures. Here we demonstrate, to the best of our knowledge, the first electrically injected GeSn vertical-cavity surface emitter on the silicon-on-insulator platform. A vertical cavity employing a buried oxide layer and a deposited SiO2 top layer as reflectors is developed for enhancing the electroluminescence in the GeSn active layer. Room-temperature electroluminescence experiments reveal clear cavity-resonant modes with adequate vertical-cavity Q-factor and greatly enhanced electroluminescence. Most importantly, under electrical injection, considerably reduced optical loss in the GeSn optical cavity was found at room temperature, toward achieving electrically injected optical gain. In addition, theoretical models for evaluating the optical gain and loss are presented for estimating net optical gain. These results on our GeSn vertical-cavity surface emitter pave the way toward efficient, continuous-wave electrically injected GeSn lasers operating at room temperature for electronic–photonic integrated circuits.

Silicon-based electronic-photonic integrated circuits, which are compatible with state-of-the-art complementary metal-oxide-semiconductor processes, offer promising opportunities for on-chip mid-infrared photonic systems. However, the lack of efficient mid-infrared optical modulators on silicon hinders the utilization of such systems. Here, we demonstrate the Franz-Keldysh effect in GeSn alloys and achieve mid-infrared electro-absorption optical modulation using GeSn heterostructures on silicon. Our experimental and theoretical results verify that the direct bandgap energy of GeSn can be widely tuned by varying the Sn content, thereby realizing wavelength-tunable optical modulation in the mid-infrared range with a figure-of-merit greater than 1.5 and a broadband operating range greater than 140 nm. In contrast to conventional silicon-photonic modulators based on the plasma dispersion effect, our GeSn heterostructure demonstrates practical and effective Franz-Keldysh mid-infrared optical modulation on silicon, helping to unlock the potential of electronic-photonic integrated circuits in a wide range of applications.

Si-based electronic-photonic integrated circuits (EPICs), which are compatible with state-of-the-art complementary metal-oxide-semiconductor (CMOS) processes, offer promising opportunities for on-chip mid-infrared (MIR) photonic systems. However, the lack of efficient MIR optical modulators on Si hinders the utilization of MIR EPICs. Here, we clearly demonstrate the Franz-Keldysh (FK) effect in GeSn alloys and achieve on-Si MIR electro-absorption optical modulation using GeSn heterostructures. Our experimental and theoretical results verify that the direct bandgap energy of GeSn can be widely tuned by varying the Sn content, thereby realizing wavelength-tunable optical modulation in the MIR range with a figure-of-merit of Δα /α0 (FOM) greater than 1.5 and a broadband operating range greater than 140 nm. In contrast to conventional silicon-photonic modulators based on the plasma dispersion effect, our GeSn heterostructure demonstrates practical and effective FK MIR optical modulation on Si and helps unlock the potential of MIR EPICs for a wide range of applications.