Functionalization of GaN Nanowire Sensors With Metal Oxides: An Experimental and DFT Investigation

摘要

The detection of NO2 molecules by GaN nanowire sensors which were functionalized with various metal oxides have been comprehensively studied with device fabrication, characterization and modeling with first-principles calculations based on density functional theory (DFT). In this work, GaN nanowires were prepared on Si substrate by standard top-down fabrication process and then fabricated into resistor based chemical sensors. The surface of GaN nanowires were functionalized by three metal oxides: TiO2, ZnO and SnO2 for analysis. The UV illuminated device characterization results indicated that the devices with TiO2 functionalization exhibited the highest response toward NO2 gas. It showed quick response (240s) and recovery (280s) process with strong NO2 selectivity. In modeling, the oxide functionalized GaN in contact with NO2 molecule was designed and geometrically optimized. Simulation results indicated that TiO2 functionalization enabled the most energy favorable surface for NO2 adsorption among the three metal oxides. In addition, the electronic properties of these oxide functionalized GaN have been studied in terms of the total density of states (TDOS) and projected density of states (PDOS), indicating an excellent agreement with the above-mentioned experimental measurements. Furthermore, the effect of environmental humidity on the adsorbate-nanocomposite interaction has been simulated and studied. Overall, the metal oxide functionalization significantly enhances the performance of GaN gas sensors and selecting an appropriate oxide will optimize the detection.