Effects of lanthanum (La) loading on the structural, optical, and electrical properties of tin monoxide (SnO) films were examined as a p-type semiconducting layer. La loading up to 1.9 atom % caused the texturing of the tetragonal SnO phase with a preferential orientation of (101), which was accompanied by the smoother surface morphology. Simultaneously, the incorporated La cation suppressed the formation of n-type SnO2 in the La-doped SnO film and widened its optical band gap. These variations allowed the 1.9 atom % La-loaded SnO film to have a high hole mobility and carrier density, compared with the La-free control SnO film. The superior semiconducting property was reflected in the p-type thin-film transistor (TFT). The control SnO TFTs exhibited the field-effect mobility (μSAT) and I ON/OFF ratio of 0.29 cm2 V–1 s–1 and 5.4 × 102, respectively. Enhancement in the μSAT value and I ON/OFF ratio was observed for the TFTs with the 1.9 atom % La-loaded SnO channel layer: they were improved to 1.2 cm2 V–1 s–1 and 7.3 × 103, respectively. The reason for this superior performance was discussed on the basis of smoother morphology, suppression of disproportionation conversion from Sn2+ to Sn + Sn4+, and reduced gap-state density.

Metal–interlayer–semiconductor contact reduces metal-induced gap states, mitigating Fermi-level pinning at metal/semiconductor interface. Here, switching property of p-type SnO FET is enhanced by increasing electron Schottky barrier at off-state.

High off-current in p-type SnO thin-film transistors (TFTs) limits the application to active matrix devices for next generation display industry. Here, we propose a new approach to suppress the off-current using metal-interlayersemiconductor (MIS) contact structure. The MIS contact structure makes Fermi-level pinning (FLP) alleviated through an ultrathin interlayer (IL) which prevents metal-induced gap states (MIGSs), the origin of severe FLP, and thereby Schottky barrier height (SBH) can be modulated. With the electron SBH (eSBH) increasing, the electron injection from drain electrode into the SnO channel is suppressed, which results in the reduction of the off-current from 5.1 × 10 -8 A to 2.4 × 10 -9 A and the enhancement of the ION/OFF from 2.7 × 10 2 to 2.8 × 10 3 compared with the conventional metal-semiconductor (MS) contacted TFTs. This work shows not only the enhancement in device performance but also a new perspective on the origin of off-current in the p-type SnO TFTs.