Zero biased Ge-on-Si photodetector with a bandwidth of 4.72~GHz at 1550~nm

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~$\mu$m Ge, with responsivities as high as 0.38 and 0.21~A/W at 1.31 and 1.55~$\mu $m, respectively. The dark current density is 0.37~mA/cm$^{2}$ and 29.4~mA/cm$^{2}$ at 0~V and a reverse bias of 0.5~V. The detector with a diameter of 30~$\mu $m, 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.