Dark-Current Suppression in Metal–Germanium–Metal Photodetectors Through Dopant-Segregation in NiGe—Schottky Barrier

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 400degC/600degC combined with a thin (~10 nm) low-temperature Si/Si_0.8 Ge_0.2 buffer layer. NiGe with DS effectively modulates the Schottky barrier height and suppresses dark current to ~10 ^-7 A at -1 V bias (width/spacing: 30/2.5 mum). Under normal incidence illumination at 1.55 mum, the devices show photoresponsivity of 0.12 A/W. The 3 dB bandwidth under - 1 V bias is up to 6 GHz.