Dark-current suppression in metal-germanium-metal photodetectors through dopant-segregation in NiGe - Schottky barrier

Abstract

We demonstrate, for the first time, the application of dopant-segregation (DS) technique in metal-germanium-metal photodetectors for dark-current suppression and high-speed performance. Low defect density and surface smooth epi-Ge (∼300 nm) layer was selectively grown on patterned Si substrate using two-step epi-growth at 400 °C/600 °C combined with a thin (∼10 nm) low-temperature Si/Si0.8Ge0.2 buffer layer. NiGe with DS effectively modulates the Schottky barrier height and suppresses dark current to ∼-7 A at -1 V bias (width/spacing: 30/2.5 μm). Under normal incidence illumination at 1.55 μm, the devices show photoresponsivity of 0.12 A/W. The 3 dB bandwidth under -1 V bias is up to 6 GHz. © 2008 IEEE.