New Insights on Factors Limiting the Carrier Transport in Very Thin Amorphous Sn-Doped In2O3 Films with High Hall Mobility

Yutaka Furubayashi,Tetsuya Yamamoto,Makoto Maehara

doi:10.1186/s11671-019-2948-4

Yutaka Furubayashi, Tetsuya Yamamoto + Show 1 more

Open Access

https://doi.org/10.1186/s11671-019-2948-4

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Abstract

We demonstrated that a mass density and size effect are dominant factors to limit the transport properties of very thin amorphous Sn-doped In2O3 (a-ITO) films. a-ITO films with various thicknesses (t) ranging from 5 to 50 nm were deposited on non-alkali glass substrates without intentional heating of the substrates by reactive plasma deposition with direct-current arc discharge. a-ITO films with t of more than 10 nm showed a high Hall mobility (μH) of more than 50 cm2/V s. For 5-nm-thick a-ITO films, we found that μH was as high as more than 40 cm2/V s. X-ray reflectivity measurement results revealed that the mass density (dm) determined the carrier transport in a-ITO films. For a-ITO films with t of more than 10 nm, dm had a high value of 7.2 g/cm3, whereas a-ITO films with t of less than 10 nm had low dm ranging from 6.6 to 6.8 g/cm3. Quantitative new insight from a size effect on the carrier transport is given for a-ITO films with t of less than 10 nm. This study shows that the ratio of t to mean free path of carrier electrons governed μH.

Highlights

Sn-doped indium oxide (ITO) has been mostly applied to transparent conducting oxide (TCO) films
We report the successful fabrication of very thin TCO films (t < 50 nm) based on amorphous-phase Tin-doped indium oxide (ITO) (a-ITO) films with a high μH by using reactive plasma deposition (RPD)
The a-ITO films with t ranging from 5 to 50 nm were fabricated with an oxygen (O2) gas flow rate (OFR) of 20 or 30 sccm without intentional heating of the substrate

Summary

Introduction

Sn-doped indium oxide (ITO) has been mostly applied to transparent conducting oxide (TCO) films. Indium oxide (In2O3) has a bixbyite crystal structure (space group Ia-3, number 206), which comprises distorted InO6 octahedra containing some oxygen defects. This is a periodic structure that produces structural vacancies (Vstr). Both an oxygen (O) and a structural vacancy are shared between adjacent polyhedra with the result that the polyhedra are joined at a corner occupied by the O, which is referred to as corner sharing hereafter. Two O atoms are shared between adjacent polyhedra with the result that the polyhedral are joined along the entire edge, referred to as edge sharing hereafter. The edge-sharing structure allows a large overlap between the wavefunctions of 5s and 5p orbitals of the valence electrons of In atoms owing to the short interatomic

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