Stress tuning of the fundamental absorption edge of pure germanium waveguides

Analysis of Optical Integration between Si3N4 Waveguide and a Ge-Based Optical Modulator Using a Lateral Amorphous GeSi Taper at the Telecommunication Wavelength of 1.55 µm

We report on the theoretical investigation of using an amorphous Ge0.83Si0.17 lateral taper to enable a low-loss small-footprint optical coupling between a Si3N4 waveguide and a low-voltage Ge-based Franz–Keldysh optical modulator on a bulk Si substrate using 3D Finite-Difference Time-Domain (3D-FDTD) simulation at the optical wavelength of 1550 nm. Despite a large refractive index and optical mode size mismatch between Si3N4 and the Ge-based modulator, the coupling structure rendered a good coupling performance within fabrication tolerance of advanced complementary metal-oxide semiconductor (CMOS) processes. For integrated optical modulator performance, the Si3N4-waveguide-integrated Ge-based on Si optical modulators could simultaneously provide workable values of extinction ratio (ER) and insertion loss (IL) for optical interconnect applications with a compact footprint.

Sn-based waveguide p-i-n photodetector with strained GeSn/Ge multiple-quantum-well active layer

We report on Sn-based p-i-n waveguide photodetectors (WGPD) with a pseudomorphic GeSn/Ge multiple-quantum-well (MQW) active layer on a Ge-buffered Si substrate. A reduced dark-current density of 59  mA/cm² was obtained at a reverse bias of 1 V due to the suppressed strain relaxation in the GeSn/Ge active layer. Responsivity experiments revealed an extended photodetection range covering the O, E, S, C, and L telecommunication bands completely due to the bandgap reduction resulting from Sn-alloying. Band structure analysis of the pseudomorphic GeSn/Ge quantum well structures indicated that, despite the stronger quantum confinement, the absorption edge can be shifted to longer wavelengths by increasing the Sn content, thereby enabling efficient photodetection in the infrared region. These results demonstrate the feasibility of using GeSn/Ge MQW planar photodetectors as building blocks of electronic-photonic integrated circuits for telecommunication and optical interconnection applications.