High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition （UHV/CVD）. This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 μm Ge, with responsivities as high as 0.38 and 0.21 A/W at 1.31 and 1.55 μm, respectively. The dark current density is 0.37 mA/cm^2 and 29.4 mA/cm^2 at 0 V and a reverse bias of 0.5 V. The detector with a diameter of 30μm, a 3 dB-bandwidth of 4.72 GHz at an incident wavelength of 1550 nm and zero external bias has been measured. At a reverse bias of 3 V, the bandwidth is 6.28 GHz.
The Si epitaxial films are grown on Si （100） substrates using pure Si2H6 as a gas source using ultrahigh vacuum chemical vapour deposition technology. The values of growth temperature Tg are 650 ℃, 700 ℃, 730 ℃, 750 ℃, and 800 ℃. Growth mode changes from island mode to step-flow mode with Tg increasing from 650 ℃ to 700℃. Rippled surface morphologies are observed at Tg = 700 ℃, 730 ℃, and 800℃, but disappear when Tg = 750℃. A model is presented to explain the formation and the disappearance of the ripples by considering the stability of the step-flow growth.
