A Ge PIN photodiode under normal incidence operating in the near infrared region is demonstrated on the silicon-on-insulator(SOI) substrate.The epitaxial Ge layers are prepared in an ultrahigh vacuum chemical vapor deposition system using low temperature Ge buffer technique.The results show that the dark current density of the device dominated by the surface leakage decreases with the mesa length increasing, and 17.2 mA/cm2 is obtained at 2 V reverse bias.A responsivity of 0.22 A/W at the wavelength of 1.31...