Three-dimensional radial-junction ZnO nanowire/a-Si:H core-shell infrared photodiodes

Hydrogenated amorphous silicon (a-Si:H)-based infrared photodiodes were fabricated by coating a-Si:H thin-film p-i-n layers over hydrothermally-synthesized disordered zinc oxide (ZnO) nanowire (NW) networks. Due to enhanced light scattering, the reversed biased three dimensional (3-D) radial-junction NW diodes showed an ∼10× increase in photocurrent under a broad spectrum (800-2000 nm) infrared (IR) illumination compared to planar devices. The diodes were optimized by using InGaZnO (IGZO) transparent top contacts that had 20% higher optical transmission in the IR compared to Al-doped ZnO electrodes. Reverse-bias dark current was minimized by optimizing the area of the NW sidewalls and the a-Si:H shell layer thickness. The former reduces the effects of carrier recombination along the NW core-shell interface and the latter minimizes the tunnelling current across the radial-junction device. An enhancement of ∼100× was achieved for these devices compared to non-optimized diodes.