We introduced photon-trapping microstructures into GeSn-based photodetectors for the first time, and achieved high-efficiency photo detection at 2 µm with a responsivity of 0.11 A/W. The demonstration was realized by a GeSn/Ge multiple-quantum-well (MQW) p-i-n photodiode on a GeOI architecture. Compared with the non-photon-trapping counterparts, the patterning and etching of photon-trapping microstructure can be processed in the same step with mesa structure at no additional cost. A four-fold enhancement of photo response was achieved at 2 µm. Although the incorporation of photo-trapping microstructure degrades the dark current density which increases from 31.5 to 45.2 mA/cm2 at −1 V, it benefits an improved 3-dB bandwidth of 2.7 GHz at bias voltage at −5 V. The optical performance of GeSn/Ge MQW photon-trapping photodetector manifests its great potential as a candidate for efficient 2 µm communication. Additionally, the underlying GeOI platform enables its feasibility of monolithic integration with other photonic components such as waveguide, modulator and (de)multiplexer for optoelectronic integrated circuits (OEICs) operating at 2 µm.

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Germanium (Ge) vertical p-i-n photodetectors were demonstrated with an ultra-low dark current of 0.57 mA/cm2 at −1 V. A germanium-on-insulator (GOI) platform with a 200-mm wafer scale was realized for photodetector fabrication via direct wafer bonding and layer transfer techniques, followed by oxygen annealing in finance. A thin germanium-oxide (GeOx) layer was formed on the sidewall of photodetectors by ozone oxidation to suppress surface leakage current. The responsivity of the vertical p-i-n annealed GOI photodetectors was revealed to be 0.42 and 0.28 A/W at 1,500 and 1,550 nm at −1 V, respectively. The photodetector characteristics are investigated in comparison with photodetectors with SiO2 surface passivation. The surface leakage current is reduced by a factor of 10 for photodetectors via ozone oxidation. The 3dB bandwidth of 1.72 GHz at −1 V for GeOx surface-passivated photodetectors is enhanced by approximately 2 times compared to the one for SiO2 surface-passivated photodetectors. The 3dB bandwidth is theoretically expected to further enhance to ∼70 GHz with a 5 µm mesa diameter.

Dark current analysis of germanium-on-insulator vertical p-i-n photodetectors with varying threading dislocation density