Impact of dopant species on the interfacial trap density and mobility in amorphous In-X-Zn-O solution-processed thin-film transistors

TL;DR

This study investigates how different dopant elements affect the interface trap density and electron mobility in amorphous In-X-Zn-O thin-film transistors, revealing correlations with electronegativity and ionic radius.

Contribution

It systematically analyzes 14 dopant elements in In-Zn-O TFTs, linking dopant properties to electrical performance and interface quality, which was not previously comprehensively studied.

Findings

Ga, Sb, and Sn doping yield highest mobility (~8.5 cm2/Vs) and low trap density.

Electronegativity and ionic radius of dopants influence interface trap density and mobility.

Certain dopants like Ca, Al, Ni, and Cu cause metallic/oxide clusters, reducing performance.

Abstract

Alloying of In/Zn oxides with various X atoms stabilizes the IXZO structures but generates electron traps in the compounds, degrading the electron mobility. To assess whether the latter is linked to the oxygen affinity or the ionic radius, of the X element, several IXZO samples are synthesized by the sol-gel process, with a large number (14) of X elements. The IXZOs are characterized by XPS, SIMS, DRX, and UV-spectroscopy and used for fabricating thin film transistors. Channel mobility and the interface defect density NST, extracted from the TFT electrical characteristics and low frequency noise, followed an increasing trend and the values of mobility and NST are linked by an exponential relation. The highest mobility (8.5 cm2/Vs) is obtained in In-Ga-Zn-O, and slightly lower value for Sb and Sn-doped IXZOs, with NST is about 2E12 cm2/eV, close to that of the In-Zn-O reference TFT. This is explained by a higher electronegativity of Ga, Sb, and Sn than Zn and In, their ionic radius values being close to that of In and Zn. Consequently, Ga, Sb, and Sn induce weaker perturbations of In-O and Zn-O sequences in the sol-gel process, than the X elements having lower electronegativity and different ionic radius. The TFTs with X = Ca, Al, Ni and Cu exhibited the lowest mobility and NST > 1E13 cm2/eV, most likely because of metallic or oxide clusters formation.