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 Ion/Ioff = 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 (ΔVT) of <1.6 V, versus <85% μ retention and ΔVT ≈ 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 (ΔHL) and metal ionic radius are the best predictors of IXZO oxygen getter efficacy.
ASJC Scopus subject areas
- Colloid and Surface Chemistry