Extraction of Density of State of Dual Gate Amorphous In-Ga-Zn-O Transistors From Meyer-Neldel (MN) Analysis

We report the effect of secondary gate bias (both the top gate voltage, VTG(V) and bottom gate voltage VBG(V) on the temperature-dependent density of state (DOS) estimation in dual gate (DG) amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). The measured transfer characteristics exhibit a negative shift with increasing secondary gate bias from 0 V to 15 V, which can be explained as the Fermi energy (EF) shift towards the conduction band (EC) edge. The extracted Meyer-Neldel energy (EMN) from temperature-dependent transfer characteristics of a-IGZO TFTs shows two trends depending on activation energy (EA); normal EMN (EA>0.1 eV) and inverse EMN (EA<0.1 eV). The secondary gate bias-independent normal EMN ~ 41 meV can be explained as the statistical shift of EF belowEC, whereas, secondary gate bias-dependent inverse EMN increases with increasing secondary gate voltage (0 V to 15 V) and appears to be due to the increased contact resistance at source/drain regions, which is confirmed by TCAD simulation. The density of tail states as a function of energy (E) is obtained from the MN rule as ~3.2×1019exp(-E/WT) with VTG, ~5.4×1019exp(-E/WT) with VBG, and a tail state slope (WT) of ~ 14.7 meV that remains independent of the applied secondary gate bias.