Germanium p-i-n photodiode on silicon for integrated photonic applications

The application of silicon photonic technologies to optical telecommunications requires the development of near-infrared detectors monolithically integrated to the Si platform. Recently, efforts in this area have focused on developing detectors from pure-Ge grown epitaxially on Si substrates. Much effort has been spent on achieving growth of high quality, relaxed Ge films for device structures, but low temperature growth and processing compatible with complementary-metal-oxide-semiconductor (CMOS) technology has yet to be achieved. In this paper, we report on p-in heterostructure photodiodes fabricated from Ge films grown directly on Si substrates using a low temperature chemical vapor deposition (CVD) process. The heterostructures were grown on arsenic-doped (n-type) Si(100) with resistivity 0.003 Omega-cm. A 350nm thick layer of intrinsic Ge was deposited first as the active region, followed by 100nm of boron-doped (p-type) Ge. Ohmic contacts were formed by evaporation of Cr and Au. The diodes were characterized with respect to their dark currents and responsivities in the near-IR. For a 60-mu m-diameter device at room temperature, the dark current densities were on the order of 10(-2) A/cm(2) and 10(3) A/cm(2) at -1V and 1V, respectively, the "turn-on" voltage was found to be 0.26 V, and the ideality factor n was found to be 1.2. The external quantum efficiency of the devices was measured at room temperature over the range 1-1.8 mu m. The responsivities at 1.3 and 1.55 mu m were found to be 0.26 and 0.11, respectively.