Comparative Study on the Effects of O₂ Flow Rate on As-Deposited Polycrystalline IAZO Films

Abstract

The research on oxide semiconductor thin-film transistors (OSTFTs) is experiencing exponential growth worldwide, aimed at enhancing the mobility, stability, film quality, and device performance while reducing the density of defect states in the channel material. In our study, we investigated indium aluminum zinc oxide (IAZO) films with varying O 2 flow rates of 25, 17, 8, and 3 sccm to optimize the channel material. Interestingly, we observed that as the flow rate of the O 2 decreased, the deposition rate increased exponentially. However, when the O 2 flow rate was set to 3 sccm, the films exhibited an extremely high density of defect states, low surface roughness, and different crystalline phases, including Zn, Al 2 O 3 , and ZnO crystals oriented in various directions. On the other hand, films deposited with an O 2 flow rate of 8 sccm demonstrated the second-highest deposition rate with high film quality, indicating a trade-off between film quality and deposition rate. Our analysis using grazing incidence X-ray diffraction and ultraviolet photoelectron spectroscopy techniques revealed very high-quality films and a low density of defect states, respectively. Remarkably, we report for the first time the successful deposition of c-axis aligned crystalline (CAAC) IAZO films at room temperature with an O 2 flow rate of 8 sccm, which exhibited the second-highest deposition rate, high film quality, low density of defect states, a comparable electron affinity (χ = 3.53 eV) to IGZO, a very high mobility (244.65 cm 2 /V•s), and a suitable carrier concentration (3.25 × 10 18 cm −3 ). CAAC-IAZO can be a potential candidate to serve as a promising channel material for enhancing device performance and addressing stability concerns in OSTFTs.