Controlled growth of gallium nitride nanowires on silicon and their utility in high performance Ultraviolet‑A photodetectors

•Growth of long, dense and uniformly thick GaN NWs by VLS process.•Fabricating GaN NWs to form MSM based UV-A photodetectors.•Upon illumination, the photo current increased several times to dark current.•The photodetector showcased ultrahigh responsivity, EQE and detectivity.•The fabricated device showcased faster switching response. [Display omitted] Device fabrication using semiconductor nanostructures for detecting ultraviolet (UV) radiations, especially UV-A (320–400 nm) has received much attention both at laboratory level and in commercial endeavours. In this work, we have attempted catalytic growth of good quality gallium nitride nanowires (GaN NWs) for utilization in building high-responsive optoelectronic devices. In order to obtain good quality control in the growth of GaN NWs, single metal catalyst has been replaced with a binary catalytic alloy of gold-palladium (Au-Pd). Scanning electron microscopy (SEM) results revealed that the NWs grown are long, dense and uniformly thick in size. The hexagonal crystal structure of the grown NWs was confirmed using x-ray diffractometer (XRD) and transmission electron microscopy (TEM). Other characterization results like x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy were helpful in determining the compositional and optical properties of the samples. The fabricated GaN NWs based UV-A photodetector showcased a fast rise time (τr) and fall time (τf) of around 22 and 29 ms, an ultrahigh responsivity (R) and sensitivity (S) of about of 11.87 × 107 A/W and 3.8 × 104%, an external quantum efficiency (EQE) of 9.45 × 109%, very high detectivity (D) of 3.83 × 1018 Jones and high wavelength selectivity in the UV-A regime.