Characteristics of Atomic Layer Deposited SnO₂ by Al Doping at Various Positions

Tin dioxide (SnO₂), which has a low melting point and wide bandgap (3.5~4.0eV), has properties suitable for applications such as transparent conductive oxide thin film transistors and active layers. However, SnO₂ has high conductivity and has the property of reducing the on/off current ratio, so research on lowering the off current is necessary to improve the electrical properties. In addition, the SnO₂ thin film contains many defects such as oxygen vacancies, making it difficult to control carriers and impurities in the thin film. The doping process using atomic layer deposition (ALD) has the advantage of reducing off-current and accurately contolling thickness. Among the dopant elements used as acceptors in SnO₂ thin films, aluminum (Al) has a higher oxidation potential (1.66V) than Sn (0.04V). Therefore, Al atoms react more strongly with oxygen than Sn, reducing oxygen vacancies in SnO₂.<br/><br/>In this study, we examined the effect of Al dopants used as the acceptor in SnO₂ with various doping positions of Al₂O₃ for lowering the oxygen vacancies and improving I_on/off ratio. Al doped SnO₂ (SnO₂:Al) thin films were deposited using thermal ALD with precursors of TDMA-Sn, TMA and O₃ as a reactant. Post-deposition annealing was carried out in an oxygen atmosphere to diffuse Al atoms uniformly and lowering oxygen vacancies of SnO₂ thin film and SnO₂:Al thin films deposited with different Al₂O₃ doping positions. The positions of Al were controlled by inserting twenty Al₂O₃ cycle into the bottom, middle, and top positions out of 121 cycles (10nm thickness) using supercycle ALD method. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical bonding state and compositions of SnO₂ thin film and SnO₂:Al thin film. It was confirmed that the SnO₂:Al thin film contained low impurity (&lt;3%) such as carbon and nitrogen. Additionally, the oxygen vacancies within the SnO₂:Al thin film reduced significantly compared to undoped SnO₂ thin film. Hall measurement analysis was examined to determine the electrical properties of SnO₂ thin film and SnO₂:Al thin film. Compared to the undoped SnO₂thin film, the carrier concentration value decreased from 4.15×10²² to 6.12×10¹⁶. Through this study, we examined the effects of various doping positions on Al-doped tin dioxide thin films by comparing their structural, chemical, and electrical properties.