Hydrogen sensitivity of ZnO p–n homojunctions

The sensor response of p-ZnO/n-ZnO structures was studied to 500 and 1000 ppm hydrogen at 300 and 400 °C. The p–n junctions behaved like tunnel diodes and were insensitive to hydrogen below 300 °C. The p-ZnO/n-ZnO junctions were fabricated by adopting techniques like d.c. sputtering (for n-ZnO) and modified CVD in a reverse spray mode (for p-ZnO), respectively. The sensitivity of the device increased and the response time decreased with increasing the operating temperature from 300 to 400 °C at each hydrogen concentration. A probable sensing mechanism has been discussed.