Meyer–Neldel Rule and Extraction of Density of States in Amorphous Indium–Gallium–Zinc-Oxide Thin-Film Transistor by Considering Surface Band Bending

In this study, we analyzed the temperature-dependent characteristics of amorphous indium–gallium–zinc-oxide (a-IGZO) thin-film transistors (TFTs). We observed that a-IGZO TFTs obey the Meyer–Neldel rule (MN rule) at low gate-to-source voltage (V GS) and the inverse MN rule at high V GS, both of which can be explained by the statistical shift of Fermi level and electrostatic potential. Large Fermi level movement for small V GS change and the inverse MN rule, which are hardly observed for conventional amorphous TFTs, indicate that there is a very low density of state (DOS) in the sub-bandgap region for a-IGZO TFTs and the performance of TFTs is not affected by contact characteristics, respectively. By using the field-effect method and considering surface band bending, we extracted the DOS in the sub-bandgap region, the distribution of which is clearly distinguished by deep and tail states. The calculated parameters for tail and deep states were N ta = 3.5 ×1017 cm-3 eV-1, E ta = 0.18 eV, N da = 1.6×1016 cm-3 eV-1, and σda = 0.21 eV.