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

摘要

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 ($sim$300 nm) layer was selectively grown on patterned Si substrate using two-step epi-growth at 400 $^{circ}$C/600 $^{circ}$C combined with a thin ( $sim$10 nm) low-temperature $hbox{Si/Si}_{0.8} hbox{Ge}_{0.2}$ buffer layer. NiGe with DS effectively modulates the Schottky barrier height and suppresses dark current to ${sim}hbox{10}^{ - 7}$ A at $-1$ V bias (width/spacing: 30/2.5  $mu$m). Under normal incidence illumination at 1.55  $mu$m, the devices show photoresponsivity of 0.12 A/W. The 3 dB bandwidth under $-1$ V bias is up to 6 GHz.