Optimization of V-Pits Forming in GaN for NO₂ Detection at Room Temperature

Gallium nitride (GaN) displays potential in the field of gas detection owing to its physical and chemical properties, such as high electron mobility, wide bandgap, and strong chemical stability. Herein, abundant V-pits on GaN (V-GaN) were successfully fabricated by KOH etching to develop a highly selective and stable NO2 gas sensor with low resistance and working temperature. The density and size of the pits were regulated by varying the etching time from 10 to 60 min. The structural and morphological properties of the prepared V-GaN gas sensors were characterized by several techniques. Among the sensors fabricated, the V-GaN gas sensor obtained following KOH etching for 50 min showed the highest response (18% at 10 ppm), response/recovery speeds (22/31 s at 10 ppm), and lowest limit of detection (LOD) (2 ppm) at room temperature (RT). The high performance displayed by this sensor was attributed to its optimal quantity of surface-active sites and maximal specific area. The sensor maintained its performance (in terms of LOD and response to NO2 gas) even under a high relative humidity. Furthermore, the V-GaN sensor exhibited outstanding selectivity and long-term stability. In addition, the resistance of the n-type V-GaN sensor developed in this study is two orders of magnitude lower than that of the p-type V-GaN sensor, and this characteristic is convenient for circuit design and actual application value.