Gas sensing properties of multiple networked GaN/WO3 core-shell nanowire sensors

GaN nanowires and GaN-core/WO3-shell nanowires were synthesized by the thermal evaporation of GaN powders followed by the sputter-deposition of WO3 and their gas sensing properties were examined. The multiple networked pristine GaN nanowire sensors showed responses of approximately 125%, 140%, 146%, 159%, and 183% to 1, 2, 3, 4, and 5 ppm NO2 gases, respectively. These responses are comparable to those obtained previously using metal oxide semiconductor one-dimensional nanostructure sensors. The responses of the nanowires to 1, 2, 3, 4, and 5 ppm NO2 gases were improved 1.3, 1.4, 1.6, 1.7 and 1.8 fold, respectively, further through the encapsulation of GaN nanowires with a WO3 thin film. The improvement in the response of GaN nanowires to NO2 gas by encapsulation is attributed to the modulation of electron transport at GaN–WO3 heterojunction. The electron transport in the core-shell nanowires is modulated by the heterojunction with an adjustable energy barrier height, resulting in an enhanced sensing property of the core-shell nanostructures.