High speed and ultra-low dark current Ge vertical p-i-n photodetectors on an oxygen-annealed Ge-on-insulator platform with GeO_x surface passivation

<jats:p>Germanium (Ge) vertical <jats:italic>p-i-n</jats:italic> photodetectors were demonstrated with an ultra-low dark current of 0.57 mA/cm<jats:sup>2</jats:sup> 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 (GeO<jats:sub>x</jats:sub>) layer was formed on the sidewall of photodetectors by ozone oxidation to suppress surface leakage current. The responsivity of the vertical <jats:italic>p-i-n</jats:italic> 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 SiO<jats:sub>2</jats:sub> 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 GeO<jats:sub>x</jats:sub> surface-passivated photodetectors is enhanced by approximately 2 times compared to the one for SiO<jats:sub>2</jats:sub> surface-passivated photodetectors. The 3dB bandwidth is theoretically expected to further enhance to ∼70 GHz with a 5 µm mesa diameter.</jats:p>