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 Ge<sub>0.91</sub>Sn<sub>0.09</sub>/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 (Al<sub>2</sub>O<sub>3</sub>) 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.
A self-aligned dry etching method was proposed and verified theoretically to enhance the magnitude and simultaneously improve the uniformity of the tensile strain in a germanium (Ge) wave-guide (WG), with the help of tensile-stressed SiN stressor at the WG sidewalls. The SiN-strained germanium-on-insulator (GOI) WG was also experimentally demonstrated. Significant tensile strain was observed in the Ge material via micro-Raman measurements. This method could potentially facilitate a Ge photodetector with its optical detection range extended further towards longer wavelength and to be comparable with that of state-of-the-art InGaAs detectors.