Effect of hydrogen plasma treatment and oxygen deficiency on conducting properties of In$_2$O$_3$:Sn thin films

TL;DR

This study investigates how hydrogen plasma treatment and oxygen deficiency affect the electrical and structural properties of In$_2$O$_3$:Sn thin films, revealing modifications in conductivity, surface structure, and electronic states.

Contribution

It provides new insights into the effects of hydrogen plasma treatment duration and oxygen deficiency on the electrical and structural properties of In$_2$O$_3$:Sn thin films.

Findings

Hydrogen plasma treatment enhances conductivity with short exposure but reduces it with longer treatment.

Oxygen deficiency increases localized states near the Fermi level, affecting conductivity.

Structural analysis shows surface modifications while bulk properties remain largely unchanged.

Abstract

Electrical conductivity, Hall effect and magnetoresistance of In$_2$O$_3$:Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, as well as the films treated in a hydrogen plasma, have been investigated in the temperature range 1.5-300 K. The observed temperature dependences of resistivity were typical for metallic transport of electrons except temperature dependence of resistivity of the In$_2$O$_3$:Sn film deposited in the oxygen deficient atmosphere. The electron concentration and mobility for the film deposited at 230$^\circ$C was larger than that for the film deposited nominally at room temperature. Short (5 minutes) treatment of the films in hydrogen plasma leads to the enhancement of electrical conductivity while longer (30 minute) treatment has the opposite effect. The electrical measurements were accompanied by AFM and SEM studies of structural properties, as well as by XPS analysis. Basic on structural and electrical measurements we conclude the reduction process initiated by the hydrogen plasma provides essential modification of the ITO films surface. At the same time, electrical properties of the remaining (located beneath the surface layer) parts of the ITO films remain mostly unchangeable. XPS analysis shows that grown in situ oxygen deficient ITO films have enhanced DOS between the Fermi level and the valence band edge. The extra localized states behave as acceptors leading to a compensation of $n$-type ITO. That can explain lower $n$-type conductivity in this material crossing over to a Mott-type hopping.