First-principles study of the atomic and electronic structures of semiconductor/insulator interfaces and transparent amorphous oxide semiconductors

Abstract

Based on the first principles density functional total energy calculations, we study the atomic and electronic properties of interface structures and the transparent amorphous oxide semiconductors. As the O-vacancy (V$_O$) defects are the most abundant defects in metal-oxides, we mainly examine the defect properties of V$_O$ defects in those systems. First, we investigate the atomic and electronic structure of the $V_O$ defects in $Si/HfO_2$ and $ZnO/HfO_2$ interfaces. The defect properties of V$_O$ are dependent on the local-geometry around the defect site. For $Si/HO_2$ interfaces, there are three different types of $V_O$ defects: $HfO_2-like$, Hf-silicate-like, and Si-dimer-like defects, considering the number of neighboring Si atoms. Unlike to the $HfO_2$ and Hf-silicate-like defects, Si-dimer-like V$_O$ defects exhibit the unoccupied anti-bonding level right below the Si conduction band minimum, which may act as electron trap in the $poly-Si/HfO_2$ gate stack. For $ZnO/a-HfO_2$ interfaces, we find that the conduction band offsets are sufficiently large, while the hole conduction barrier is negligible. There exist O-dangling bonds at the interface. In case of n-type ZnO, they are inactive due to deep level nature. Similarly, V$_O$ defects are found to be inactive in the ZnO channel region, whereas those in the gate oxide may act as electron and hole traps, causing the threshold voltage instabilities under gate bias, similar to Si/HfO$_2$. Both in the $Si/HfO_2$ and $ZnO/HfO_2$ interfaces, the $V_O$ defects tend to segregate toward the interface due to large atomic relaxations of atoms near the interface. Next, we expand our investigations into the study of the atomic and electronic properties of transparent amorphous oxide semiconductor (transparent AOS; TAOS). We generate various amorphous structures, where In, Sn, B, Ga, and Hf atoms incorporated in the ZnO, forming In-Ga-Zn-O (IGZO), Zn-Sn-O (ZTO), B-Zn-Sn-O, and Hf-In-Zn-O (HIZO), and the atomic and ele...