Enhancement of H2 gas sensing properties of ZnO films by Mg alloying

Abstract To examine the effect of Mg addition on the gas sensing properties of ZnO, MgxZn1-xO epitaxial films with a constant thickness, in-plane crystal grain size, and surface morphology and varying Mg contents were prepared by pulse laser deposition, and their gas sensing properties were investigated. The results showed that the response to H2 gas improved as the number of Mg atoms substituted into Zn sites increased. In addition, as the thickness of MgxZn1-xO films with the optimal Mg content decreases, the sensor response increases remarkably. A sensor with a thickness of 9 nm showed a maximum response value of approximately 3000 to 800 ppm H2. To determine why the sensor response was improved by the addition of Mg, MgO-particle-deposited undoped ZnO films and c-axis-oriented MgxZn1-xO films with random in-plane rotation domains were prepared, and the characteristics of these sensors were compared with those of the epitaxial MgxZn1-xO films. We identified two causes for the improved sensing properties: a reduced residual electron concentration in the films due to the substitution of Mg and the chemical sensitization effect of Mg atoms. This study also suggested that a decrease in electron mobility results in a decreased sensor response value.