Lanthanum Doping Enabling High Drain Current Modulation in a p-Type Tin Monoxide Thin-Film Transistor

Abstract

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 (μ_SAT) and <i>I</i>_ON/OFF ratio of 0.29 cm² V^-1 s^-1 and 5.4 × 10², respectively. Enhancement in the μ_SAT value and <i>I</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.