In this work, metal-semiconductor-metal photodetectors (MSM PDs) on a GeSn-on-insulator (GeSnOI) platform were demonstrated. This platform was realized by direct wafer bonding (DWB) and layer transfer methods using 9% Sn composition of GeSn film epitaxial-grown on Si. The compressive strain in the GeSn film was observed as ~0.23%, which indicates a significant reduction of the strain compared to the ~5.5% lattice mismatch at an interface of the Ge0.91Sn0.09/Si. GeSn MSM PDs demonstrated on a GeSnOI platform displayed a low dark current of 4nA at a 1V of bias voltage due to the insertion of a thin aluminum oxide (Al2O3) layer in an interface of metal/GeSn for an alleviation of Fermi-level pinning. The responsivity was 0.5 and 0.29 A/W at the wavelength of 1,600 and 2,033nm at 2V, respectively. This work paves the way for GeSnOI photonics as the next promising platform along with Si-on-insulator (SOI) and Ge-on-insulator (GOI) platforms for mid-infrared (MIR) communication and sensing applications.
Silicon photonics has traditionally focused on near infrared wavelengths, with tremendous progress seen over the past decade. However, more recently, research has extended into mid infrared wavelengths of 2 μm and beyond. Optical modulators are a key component for silicon photonics interconnects at both the conventional communication wavelengths of 1.3 μm and 1.55 μm, and the emerging mid-infrared wavelengths. The mid-infrared wavelength range is particularly interesting for a number of applications, including sensing, healthcare and communications. The absorption band of conventional germanium photodetectors only extends to approximately 1.55 μm, so alternative methods of photodetection are required for the mid-infrared wavelengths. One possible CMOS compatible solution is a silicon defect detector. Here, we present our recent results in these areas. Modulation at the wavelength of 2 μm has been theoretically investigated, and photodetection above 25 Gb/s has been practically demonstrated.
We present a library of high-performance passive and active silicon photonic devices at the C-band that is specifically designed and optimized for edge-coupling-enabled silicon photonics platform. These devices meet the broadband (100 nm), low-loss (< 2dB per device), high speed (≥ 25 Gb/s), and polarization diversity requirements (TE and TM polarization extinction ratio ≤ 25 dB) for optical communication applications. Ultra-low loss edge couplers, broadband directional couplers, high-extinction ratio polarization beam splitters (PBSs), and high-speed modulators are some of the devices within our library. In particular, we have designed and fabricated inverse taper fiber-to-waveguide edge couplers of tip widths ranging from 120 nm to 200 nm, and we obtained a low coupling loss of 1.80±0.28 dB for 160 nm tip width. To achieve polarization diversity operation for inverse tapers, we have experimentally realized different designs of polarization beam splitters (PBS). Our optimized PBS has a measured extinction ratio of ≤ 25 dB for both the quasiTE modes, and quasi-TM modes. Additionally, a broadband (100 nm) directional coupler with a 50/50 power splitting ratio was experimentally realized on a small footprint of 20×3 μm2 . Last but not least, high-speed silicon modulators with a range of carrier doping concentrations and offset of the PN junction can be used to optimise the modulation efficiency, and insertion losses for operation at 25 GHz.