A Comparative Study of InSnZnO Transparent Thin-Film Transistors With AZO and GZO Electrodes

Indium-tin-zinc oxide (InSnZnO) transparent thin-film transistors (TTFTs) using aluminum-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO) as electrodes are investigated in this study. First, the sputtering power for both AZO and GZO is optimized based on their specific contact resistivity. The work functions of AZO, GZO, and InSnZnO, respectively, are 4.47, 4.26, and 4.42 eV as measured by ultraviolet photoelectron spectroscopy (UPS). The higher work function of AZO compared to InSnZnO shows the formation of a Schottky junction, while the lower work function of GZO compared to InSnZnO indicates the formation of an ohmic contact. This distinction in junction types results in GZO/InSnZnO displaying a lower specific contact resistivity of
$0.43~\Omega $
-cm2, in contrast to the higher specific contact resistivity observed in AZO/InSnZnO, measured at
$5.04~\Omega $
-cm2. The lower specific resistivity of GZO makes TTFT shows lower ON-state resistance of 8.85
$\text{k}\Omega $
and higher field-effect mobility of 38.85 cm
$^{{2}}\cdot \text{V}^{-{1}}\cdot \text{s}^{-{1}}$
. Furthermore, it is found that TTFTs using GZO as electrodes exhibit stable electrical characteristics after negative bias illumination stress (NBIS) for 10 800 s since GZO has smaller optical transmittance than AZO. Therefore, GZO is better than AZO to serve as the electrodes of InSnZnO TTFT.