High speed vertical GeSn photodiodes on Si

Vertical GeSn pin photodiodes with Sn content of 0 %, 2 % and 4.2 %, resp., grown with molecular beam epitaxy on thin Ge virtual substrates on Si are investigated by using the electrical and optoelectrical methods: direct current, light responsivity and optical high frequency (40 GHz). The vertical photodiodes were fabricated with a double mesa process. The mesa radii are between 5 μm and 80 μm. For a laser wavelength of 1550 nm an increase of the optical responsivities (84 mA/W-218 mA/W) for the vertical photodiodes with thin (300 nm) absorbers as function of the Sn content is found. The optical high frequency bandwidth of all photodiodes with 5 μm radius is above 40 GHz at enough reverse voltage [1].