Conductometric gas sensor based on p-type GaN hexagonal pits /PANI for trace-level NH3 detection at room temperature

Herein, we demonstrate two ammonia (NH3) gas sensors based on p-type Gallium nitride (GaN) hexagonal pits (GaN-HP)/ Polyaniline (PANI) heterostructure prepared by wet etching process and in situ polymerization. The morphologies, structures of p-type GaN-HP/PANI sensors based on planer p-type GaN with etching time for 20 min and 30 min (GaN-HP/PANI-1 and GaN-HP/PANI-2) have been characterized. The responses of GaN-HP/ PANI-1 and GaN-HP/PANI-2 are 3.2 and 6.3 times higher than that of pure PANI at room temperature, which is primarily due to the gas sensing improvement effect of p-p junction between p-type GaN-HP and PANI. Moveover, the GaN-HP/PANI-2 shows 1.94-fold enhancement in the gas sensing response toward 100 ppm NH3 and lower detection limits than that of GaN-HP/PANI-1, indicating that its performance is highly dependent on the etching time. Compared to GaN-HP/PANI-1, the excellent improvement of gas sensing for GaN-HP/PANI-2 can be attributed to the higher specific surface area, the stronger protonation degree of PANI and synergistic effects of the p-p junction effect. Furthermore, the selectivity, repeatability and the effect of relative humidity on the gas sensing performances of the two both sensors have also been explored. This work can provide a helpful reference for development of high-performance GaN-HP/PANI based gas sensors.