Large-area silicon nanowire Schottky junction photodetector with tunable absorption and low junction capacitance

Silicon photodetectors for operation in the near-infrared with a sufficient responsivity and high-speed operation are currently needed as scalable, CMOS compatible components for photonic and communication applications. Photodetectors based on semiconductor nanowire structures with dielectric planarization enable larger active optical areas and higher operating speeds than planar devices due to reduced junction capacitance and enhanced absorption. Here, we report on the fabrication and characterization of a silicon nanowire photodetector with dielectric infilling and a transparent indium tin oxide (ITO) Schottky contact. Optical simulations show that the absorbed power can be confined at the top of the nanowire array, enabling efficient operation in the near-infrared. This is despite the relatively low absorption coefficient for silicon in this wavelength range in addition to the design of the nanowire array to have a low fill factor compared to the bulk material in order to minimize the junction capacitance. The responsivity of this device is  >0.3 A W⁻¹ at a reverse bias of 2 V and the junction capacitance is 8  ±  2 nF cm⁻², which are respectively comparable and lower than the values expected for a planar silicon Schottky junction photodetector with a similar active area. (paper)