Integrated germanium optical interconnects on silicon substrates

Journal name:
Nature Photonics
Year published:
Published online


Monolithic integration of optoelectronics with electronics is a much-desired functionality. Here, we demonstrate that it is possible to realize low-loss Ge quantum-well photonic interconnects on Si wafers. We show that Ge-rich Si1–xGex virtual substrates can act as a passive, high-quality optical waveguide on which low-temperature, epitaxial growth of Ge quantum-well devices can be realized. As a proof of concept, the photonic integration of a passive Si0.16Ge0.84 waveguide and two Ge/SiGe multi-quantum-well active devices, an optical modulator and a photodetector was realized to form a photonic interconnect using a single epitaxial growth step. This demonstration confirms that Ge quantum-well interconnects are feasible for low-voltage, broadband optical links integrated on Si chips. Our approach can be extended to any kind of Ge-based optoelectronic device working within telecommunication wavelengths as long as a suitable Ge concentration is selected for the Ge-rich virtual substrate.

At a glance


  1. Epitaxial growth and its HR-XRD characterization
    Figure 1: Epitaxial growth and its HR-XRD characterization

    a, Schematic of the Ge/SiGe MQWs and SiGe waveguide stacks grown on a Si substrate via a graded buffer by LEPECVD. b, X-ray diffraction ω–2θ scan along the [001] direction through the (004) Bragg peak. The intensity is integrated along a Qy range of 0.025 Å−1. c,d, RSMs in the vicinity of the (224) (c) and (004) (d) reflections. Qy and Qz indicate longitudinal and perpendicular components of the momentum transfer, respectively.

  2. Schematic and scanning electron microscopy (SEM) views of the three kinds of
                    photonic device fabricated on the same chip and with the same process
    Figure 2: Schematic and scanning electron microscopy (SEM) views of the three kinds of photonic device fabricated on the same chip and with the same process flows.

    a, Si0.16Ge0.84 rib waveguides (2 µm wide, 1.5 µm high and 1 µm etched) of different lengths for propagation loss characterization. Lower inset: film mode-matching simulation showing the single-mode condition of the TE-polarized guided light. b, A stand-alone 4-µm-wide and 100-µm-long Ge/SiGe MQW p–i–n diode. c, Fabricated photonic interconnect consisting of a passive Si0.16Ge0.84 waveguide and active Ge/Si0.16Ge0.84 MQW optical modulator and photodetector (the taper section is 55 µm long).

  3. Characterizations of the Si0.16Ge0.84
    Figure 3: Characterizations of the Si0.16Ge0.84 waveguides.

    a, Measured transmitted optical power versus waveguide length at different wavelengths. b, Propagation loss of the fabricated Si0.16Ge0.84 waveguides (Fig. 2a) obtained via a cut-back method.

  4. Characterizations of the stand-alone
                        Ge/Si0.16Ge0.84 MQWs modulator and
    Figure 4: Characterizations of the stand-alone Ge/Si0.16Ge0.84 MQWs modulator and photodetector.

    a,b, Photocurrent spectra (a) and extinction ratio (b) versus absorption loss obtained from transmission measurements at different bias voltages of the 4-µm-wide and 100-µm-long Ge/Si0.16Ge0.84 MQWs (Fig. 2b) grown on top of the Si0.16Ge0.84 layer. Strong QCSE is obtained at wavelengths longer than 1,420 nm, where the underlying Si0.16Ge0.84 layer can act as a low-loss waveguide, as shown in Fig. 3. c,d, Optical detection (c) and optical modulation bandwidths (d) of the Ge/Si0.16Ge0.84 MQWs device.

  5. Characterizations of the integrated optical interconnects of a passive
                        Si0.16Ge0.84 waveguide and active
                        Ge/Si0.16Ge0.84 MQW modulator and
    Figure 5: Characterizations of the integrated optical interconnects of a passive Si0.16Ge0.84 waveguide and active Ge/Si0.16Ge0.84 MQW modulator and photodetector.

    a, IV characteristics without illumination (dark current) of the Ge/SiGe MQWs integrated on a Si0.16Ge0.84 waveguide (Fig. 2c) for ten randomly selected devices. b, IV characteristics of the fabricated photonic interconnect (Fig. 2c), when the first device is used as an optical modulator and the second device as a photodetector. c, Photocurrents at the photodetector with different reverse-bias voltages at the optical modulator; 5 µA and 10 µA modulations are obtained at the photodetector with 1 V swing (between 1 and 2 V) and 3 V swing (between 0 and 3 V) applied at the optical modulator. The photodetector bias is −1 V and the dark current is 10 nA. Inset: similar performance can be obtained for a wide spectral range from 1,430 nm to 1,450 nm.


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Author information


  1. Institut d'Electronique Fondamentale, Université Paris-Sud, CNRS UMR 8622, Bâtiment 220, 91405 Orsay Cedex, France

    • Papichaya Chaisakul,
    • Delphine Marris-Morini,
    • Mohamed-Said Rouifed,
    • Paul Crozat &
    • Laurent Vivien
  2. L-NESS, Dipartimento di Fisica del Politecnico di Milano, Polo di Como, Via Anzani 42, I-22100 Como, Italy

    • Jacopo Frigerio,
    • Daniel Chrastina,
    • Stefano Cecchi &
    • Giovanni Isella


P.Ch., D.M.-M. and L.V. conceived the project. P.Ch. designed and fabricated the tested devices, conducted the experiments and performed optical simulations. P.Ch. and D.M.-M. analysed the experimental data. J.F. carried out epitaxial growth and band diagram calculations. D.C. and S.C. performed HR-XRD measurements and analysis. S.C. participated in the epitaxial growth. P.Cr. participated in device characterization. All authors contributed to manuscript preparation. D.M.-M., G.I. and L.V. supervised the project.

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