Ni-pattern guided GaN nanowire-array humidity sensor with high sensitivity enhanced by UV photoexcitation

Selective-area lateral GaN nanowire array has been one-step fabricated over large scale by Ni-pattern guided chemical vapor deposition (CVD) growth. Two neighboring Ni electrodes, acting as source and drain, can be bridged across by a plenty of GaN nanowires. Based upon this architecture, the self-formed GaN nanowire-array humidity sensor exhibits the typical Schottky-contacted metal-semiconductor-metal (MSM) characteristic, which has a great dependence on the adsorption of water molecules. As increasing the relative humidity (RH) in the moisture environment, its output current has a sharp decrease from 29.3 to 0.913 μA and from −16.8 to −0.215 μA when biased at 5 and −5 V respectively, exhibiting its ultrahigh RH sensing above two orders of magnitude. By ultraviolet (UV) illumination, the optical absorption of GaN nanowire can produce a large number of photogenerated carriers, which may effectively modulate its electrical conductivity and surface depletion. Correspondingly, its RH sensitivity has been largely enhanced by UV photoexcitation from 3208% to 10,066% at 5 V and from 7818% to 24,037% at −5 V, respectively. It manifests that the surface depletion or surface potential may be effectively modulated by both the humidity adsorption and UV photoexcitation. Therefore, the optical absorption enhancement of GaN nanowire array may provide a promising approach for highly sensitive humidity, gas or biological sensing applications.