Role of peroxo O22− and ozonide O3− ions in the conduction mechanism of a-ZnSnO films

This work explores how annealing influences the properties of ultrathin amorphous zinc tin oxide (38 nm thick a-ZTO) thin films fabricated by magnetron sputtering. The samples were subjected to post-deposition annealing at temperatures between 200 °C and 300 °C in an oxidizing environment, consisting of an O 2 /N 2 gas mixture. During the annealing process, the sheet resistance of the films was continuously monitored using in situ measurements. In-situ monitoring reveals a transition from semiconducting to metallic-like transport as the resistivity reaches its minimum. Optimized annealing yields films with conductivity up to 430 S cm − 1 , carrier concentration 1 . 5 × 1 0 20 cm − 3 , and mobility 19 cm 2 V − 1 s − 1 , without compromising optical properties. Complementary density functional theory (DFT) calculations suggest that the formation of oxygen-related species such as peroxo (O 2 2 − ) and ozonide (O 3 − ) groups play a role in modifying the electronic structure and contributing to carrier transport, while the dominant effect arises from defect reorganization and mobility enhancement.