Optimal Aluminum Doping Method in PEALD for Designing Outstandingly Stable InAlZnO TFT

Abstract

Oxide semiconductors are promising semiconducting materials for next-generation thin-film transistors (TFTs). The role of the cations should be considered in the design of oxide semiconductors suitable for various applications. Ga has been widely used as a carrier suppressor in oxide semiconductors; however, research has recently been conducted to replace it with Al, which is cheaper and forms a stronger bond with O. Deposition using plasma-enhanced atomic layer deposition (PEALD) is very useful for controlling the composition of the cations in an oxide semiconductor. In this study, an InAlZnO (IAZO) semiconductor was deposited using super-cycle PEALD for the first time. Al2O3 (AO), AlZnO (AZO), and InAlO (IAO) as Al doping layers in IAZO are evaluated. Considering its electrical characteristics and stability, AZO is selected as the optimal Al doping layer. The IAZO thin film and TFT characteristics according to the Al doping method are examined through the role of the cations and H concentration. In addition, the Al concentration is controlled by adjusting the number of cycles in super-cycle PEALD. As the Al concentration decreased, the mobility increased; however, the stability degraded significantly, which is induced by the increase in oxygen vacancies. Finally, the high-Al IAZO system using AZO successfully showed overall excellent properties including mobility over 10 cm(2) V-1 s, and outstanding stability under 0.1 V, which are greatly improved compared to previously reported IAZO TFTs.