Fabrication of high-Performance humidity sensors based on KCl-modified GaN nanorods for respiratory monitoring

In this study, gallium oxide hydroxide (GaOOH) nanorods were synthesized using a hydrothermal method, which was followed by a high-temperature nitriding process to synthesize gallium nitride (GaN) nanorods. Then, potassium chloride (KCl)-modified GaN nanorod composite materials were prepared using the physical mixing method. The analysis of the humidity sensitivity test demonstrated that the KCl/GaN nanorods with a KCl loading of 2.5 wt% exhibited the best humidity sensitivity, with a resistance change response of 36589.59 under 97% relative humidity (RH), which was 2.51 times that of pure GaN nanorods without KCl doping. The response and recovery times of the KCl/GaN-2.5- wt% nanorod humidity sensor in a 97%-RH environment were 3 s and 80 s, respectively. The response time did not exhibit considerable fluctuations compared with the undoped GaN nanorods, and the recovery time increased. The hierarchical morphology of the GaN nanorods created abundant adsorption sites for water molecules, while the incorporation of KCl enhanced the electrical conductivity of the composite material, thereby resulting in an increase in the magnitude of the resistance changes of the sensor in environments with different humidity conditions. The sensor also demonstrated excellent repeatability and long-term stability, making it suitable for applications in respiratory monitoring.