Oxygen "getter" effects on microstructure and carrier transport in low temperature combustion-processed a-InXZnO (X = Ga, Sc, Y, La) transistors

In oxide semiconductors, such as those based on indium zinc oxide (IXZO), a strong oxygen binding metal ion ("oxygen getter"), X, functions to control O vacancies and enhance lattice formation, hence tune carrier concentration and transport properties. Here we systematically study, in the IXZO series, the role of X = Ga³⁺ versus the progression X = Sc ³⁺ → Y³⁺ → La³⁺, having similar chemical characteristics but increasing ionic radii. IXZO films are prepared from solution over broad composition ranges for the first time via low-temperature combustion synthesis. The films are characterized via thermal analysis of the precursor solutions, grazing incidence angle X-ray diffraction (GIAXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging. Excellent thin-film transistor (TFT) performance is achieved for all X, with optimal compositions after 300 C processing exhibiting electron mobilities of 5.4, 2.6, 2.4, and 1.8 cm² V^-1 s^-1 for Ga³⁺, Sc³⁺, Y³⁺, and La ³⁺, respectively, and with I_on/I_off = 10 ⁷-10⁸. Analysis of the IXZO TFT positive bias stress response shows X = Ga³⁺ to be superior with mobilities (μ) retaining >95% of the prestress values and threshold voltage shifts (ΔV_T) of <1.6 V, versus <85% μ retention and ΔV_T ≈ 20 V for the other trivalent ions. Detailed microstructural analysis indicates that Ga³⁺ most effectively promotes oxide lattice formation. We conclude that the metal oxide lattice formation enthalpy (ΔH_L) and metal ionic radius are the best predictors of IXZO oxygen getter efficacy.