Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility.

A. Malasi,A. Baddorf,M. Patel,B. Lawrie,H. Taz,R. Pooser,R. Kalyanaraman,G. Duscher,A. Farah

doi:10.1038/srep18157

Abstract

Here we report that ternary metal oxides of type (Me)2O3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 104 S/m) and Hall mobility (>30 cm2/V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV. This material shows emergent semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. Since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned.

Highlights

We show the first evidence of a ternary amorphous oxide semiconductor that goes beyond this existing paradigm of requiring metal cations with (n-1)d10ns[0] in order to show good conduction
Based on the substantial knowledge developed over the past decade, it is possible to summarize two common features found in all the ternary amorphous oxides that show high mobility (> 10 cm2/V-s), such as the as In-Ga-Zn oxide (a-IGZO) system
Overlap of the large spherically symmetric ns levels involved in the metal cation bonding produces large s-conduction band curvature and a high mobility for carriers excited from the valence band formed by oxygen 2p states[7,9]

Summary

Introduction

We show the first evidence of a ternary amorphous oxide semiconductor that goes beyond this existing paradigm of requiring metal cations with (n-1)d10ns[0] in order to show good conduction. This novel oxide material consists of the metals Fe, Tb and Dy whose common oxidation states involve partly filled d-subshells (3d54s0 for Fe) or f-subshells (4f96s0 for Tb and 4f106s0 for Dy) and are normally d- or f-band insulating oxides[11,12]. We found that films made at room temperature by pulsed laser deposition from a metallic target, followed by oxidation by ambient exposure, were amorphous, had very high visible light transparency (> 90%), high thermal stability of the amorphous phase, very high electronic conductivity (> 5 × 104 S/m), and extraordinarily high as-prepared Hall mobilities of > 30 cm2/V-s, a combination of properties that already rivals that of the best known Indium-based amorphous oxide semiconductors[2]

Methods

Results

Conclusion