Suppression of dark current in germanium-tin on silicon p-i-n photodiode by a silicon surface passivation technique

We demonstrate that a complementary metal-oxide-semiconductor (CMOS) compatible silicon (Si) surface passivation technique effectively suppress the dark current originating from the mesa sidewall of the Ge_0.95Sn_0.05 on Si (Ge_0.95Sn_0.05/Si) p-i-n photodiode. Current-voltage (I-V) characteristics show that the sidewall surface passivation technique could reduce the surface leakage current density (J_surf) of the photodiode by ∼100 times. A low dark current density (J_dark) of 0.073 A/cm² at a bias voltage of -1 V is achieved, which is among the lowest reported values for Ge_1-xSn_x/Si p-i-n photodiodes. Temperature-dependent I-V measurement is performed for the Si-passivated and non-passivated photodiodes, from which the activation energies of dark current are extracted to be 0.304 eV and 0.142 eV, respectively. In addition, the optical responsivity of the Ge_0.95Sn_0.05/Si p-i-n photodiodes to light signals with wavelengths ranging from 1510 nm to 1877 nm is reported.