Subgap states in aluminium- and hydrogen-doped zinc-oxide thin-film transistors

Abstract

This study presents the Al2O3-induced hydrogen and aluminum doping effects in atomic-deposited ZnO films. Bottom-gate ZnO thin-film transistors (TFTs) show n-type enhancement-mode transfer characteristics. However, when equipped with the top...

Subthreshold Conduction of Disordered ZnO-Based Thin-Film Transistors

“…Hence, to unveil the effects of the disordered electronic features of the ZnO films on the degradation, we tried to modify the subthreshold current of Equation (5). Please note that, unless we use van der Waals electrodes such as graphene, capacitance–voltage ( C–V )-based methods would be challenging to use for the extraction of the interfacial trap capacitance due to the doping effects from the top electrodes such as aluminum [ 22 ]. First, we tried to include the non-uniform and gate-dependent interface trap capacitance ( C it ) factor in the relation since the charges of the disordered semiconductors mainly transport via the localized trap states [ 25 ].…”

“…Furthermore, to gain insights into the subthreshold conduction of the disordered ZnO TFTs, we investigated and carefully analyzed the temperature-dependent current–voltage characteristics of the ZnO TFTs from 180 to 300 K. Figure 5 a shows the temperature-dependent transfer characteristics of the ZnO TFTs. By assuming that the gate-dependent activation energy ( E a ) is closely related to the energetic difference between the Fermi level and conductive states, the gate-dependent activation energy can be extracted using the Meyer–Neldel rule of I ( V gs ) = I 0 exp(− E a / kT ), as in the inset of Figure 5 a [ 22 , 39 ]. From the gate-dependent activation energy, the areal density of states, DOS, g ( E ) can be deduced using the relation of g ( E ) = qC i ( dE a / dV gs ) −1 , as in Figure 5 b [ 40 , 41 ].…”

“…Additionally, capacitance–voltage ( C–V ) based methods such as the low- and high-frequency methods [ 15 , 16 ], the conductance method [ 17 ], and the charge pumping method [ 18 ] could be used for characterizing the subthreshold characteristics of the disordered semiconductors. However, it should be carefully applied since the deposition of electrodes such as aluminum can cause electron doping on the oxide semiconductors, which alters the subthreshold characteristics [ 19 , 20 , 21 , 22 ]. Furthermore, due to the low capacitance of the generally used Si/SiO 2 wafers (<~20 n Fcm −2 ), the capacitance changes from the interface or semiconductor traps would be hardly probed.…”