Enhanced adsorption properties of ZnO/GaN heterojunction for CO and H2S under external electric field

The adsorption and electronic properties of CO and H2S adsorbed on ZnO/GaN heterojunction under external electric field (Eext) are investigated by first principle calculations. When the positive Eext is applied, the direction of the built-in electric field and the positive Eext are the same, the adsorption energy (Ead), charge transfer, and bandgap are increased. The positive (negative) breakdown voltages of CO and H2S gases adsorbed on heterojunction are −1.0 V/Å (0.7 V/Å) and −0.7 V/Å (1.2 V/Å), respectively. Interestingly, when a positive and negative Eext is applied, H2S gas is acted as the donor and acceptor, respectively. The ZnO/GaN heterojunction is selective for H2S gas when both CO and H2S are simultaneously adsorbed. When the positions of the gases are exchanged, it is not until the Eext is increased to ±0.2 V/Å that the adsorption process became spontaneous. The larger the Eext is applied, the greater the Ead of gas. It is a more than 150 % and 200 % increase for CO and H2S gases as compared to the absence of Eext. These results reveal that the ZnO/GaN heterojunction can serve as the candidate materials for the high sensitivity gas sensors.