Strain Control of a NO Gas Sensor Based on Ga-Doped ZnO Epilayers

The properties of gas sensors based on Ga-doped ZnO epilayers grown by metalorganic chemical vapor deposition with dislocation and strain control inside the active layer have been investigated. The gas sensor device based on a Ga-doped ZnO epilayer with a lower TEGa flow rate presents better performance for NO sensitivity than based on a Ga-doped ZnO epilayer with higher TEGa flow. It could be due to Ga source deficiency during the film formation, which results in the higher dislocation density in the ZnO epilayer. In our devices, the best performing device has a NO sensitivity of 23.653 under a 2.5 ppm NO environment. Furthermore, the sensitivities are 5.321, 1.692, 3.320, 1.000, 1.066, and 1.163 for our device with the atmosphere of NO (500 ppb), NO2 (500 ppb), CO (100 ppm), CO2 (1500 ppb), SO2 (100 ppm), and NH3 (100 ppm), respectively. In this work, the stain of the activated film is quantified by high-resolution lattice images, and the higher strain value sample performs better NO sensitivity than others. The result is correlated to the amount of dangling bond inside the activated layer and highly relevant to a proposed strain quantification method. Finally, our device still has a sensitivity as a NO gas concentration lowers to 25 ppb, which is promising for future medical applications.