Alloying of In/Zn oxides with various X atoms stabilizes the IXZO structures
but generates electron traps in the compounds, degrading the electron mobility.
To assess whether the latter is linked to the oxygen affinity or the ionic
radius, of the X element, several IXZO samples are synthesized by the sol-gel
process, with a large number (14) of X elements. The IXZOs are characterized by
XPS, SIMS, DRX, and UV-spectroscopy and used for fabricating thin film
transistors. Channel mobility and the interface defect density NST, extracted
from the TFT electrical characteristics and low frequency noise, followed an
increasing trend and the values of mobility and NST are linked by an
exponential relation. The highest mobility (8.5 cm2/Vs) is obtained in
In-Ga-Zn-O, and slightly lower value for Sb and Sn-doped IXZOs, with NST is
about 2E12 cm2/eV, close to that of the In-Zn-O reference TFT. This is
explained by a higher electronegativity of Ga, Sb, and Sn than Zn and In, their
ionic radius values being close to that of In and Zn. Consequently, Ga, Sb, and
Sn induce weaker perturbations of In-O and Zn-O sequences in the sol-gel
process, than the X elements having lower electronegativity and different ionic
radius. The TFTs with X = Ca, Al, Ni and Cu exhibited the lowest mobility and
NST > 1E13 cm2/eV, most likely because of metallic or oxide clusters formation