Fabrication and performance of Ge-on-Si PIN photodetectors

With the maturity of germanium (Ge) growth on Si, Ge photodetectors have drawn great interests worldwide, which are potentially used in NIR/MIR light detecting, optical telecommunications, single photon detecting, biosensor applications. Lateral and vertical structured Ge-on-Si PIN photodetectors were fabricated and investigated. A dark current density of 20.4 mA/cm² was obtained, and small size devices resulted in low dark current values. The responsivity as a function of the wavelength was tested, and the highest responsivity of 0.8 A/W at the wavelength of 1310nm was obtained in vertical structured photodetectors, while the lateral structured photodetectors had the best 3dB bandwidth of 0.5 GHz, which was evaluated from the response time of 0.7 ns. The quantum efficiency was ~76%, and the reason of low 3dB bandwidth was discussed.