High-specific-detectivity, low-dark-current Ge nanowire metal–semiconductor–metal photodetectors fabricated by Ge condensation method

We have investigated Ge nanowire (NW) metal–semiconductor–metal (MSM) photodetectors with high specific detectivity and low dark current, in which various sizes Ge NWs were fabricated by three-dimensional (3D) Ge condensation techniques. It has been demonstrated that the photocurrent gain increases significantly from 6.31  ×  10⁴ to 4.47  ×  10⁶ with the reduction of Ge NW width from 170 to 35 nm. A low dark current of 5.1 nA and an ultra-high specific detectivity of 1.26  ×  10¹⁴ cm·Hz^1/2·W⁻¹ at 560 nm under 0.51 V bias are achieved for the 35 nm wide Ge NW photodetector. It has been proposed that the interface states provided by SiGeO_x formed during Ge condensation process serve as electron traps to generate photogating effect, resulting in high photocurrent gain and high specific detectivity in the MSM photodetector. The fully complementary metal-oxide-semiconductor (CMOS) compatible and scalable process suggests a great potential of the Ge NW for low cost, high performance near infrared photodetectors. (paper)