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 = Sc3+ -> 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 degrees 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 La23+, respectively, and with I-on/I-off = 107-108. Analysis of the LXZO TFT positive bias stress response shows X = Ga3+ to be superior with mobilities (mu) retaining >95% of the prestress values and threshold voltage shifts (Delta V-T) of < 1.6 V, versus < 85% mu retention and Delta V-T approximate to 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 (Delta H-L) and metal ionic radius are the best predictors of IXZO oxygen getter efficacy.