Franz-Keldysh Effect in GeSn Detectors

Four different GeSn photodetectors with Sn content up to 5.6 % are investigated. From current-voltage measurements with and without illumination, the spectral optical responsivity is determined. With the responsivity and the measured reflection, the absorption and the direct band gap energies are calculated. All four samples show a voltage dependent change of the absorption due to the Franz-Keldysh effect. At a wavelength of 1950 nm, a maximum absorption ratio of 2 is observed for 4.2 % Sn for a voltage swing of 2.5 V