Photovoltaic Effect De-Embedded Photonic C-V Characterization of Subgap Density of States in Amorphous Oxide Semiconductor Thin-Film Transistors

Abstract

The subgap density of states $\textit{g}_{\text{DOS}}$ (E) is a critical parameter governing the electrical characteristics and short-/long-term reliability of amorphous oxide semiconductor thin-film transistors (AOS TFTs). In this study, we propose an advanced technique for g(DOS) (E) in AOS TFTs through the photonic capacitance-voltage (C-V) characterization. We focused on the gate voltage (V-G) dependence of the photovoltaic effect (PVE), which has not been considered in previous studies. The PVE strongly depends on the amount of g(DOS)(E) reacting in each energy interval, requiring the consideration of V-G -dependency. Furthermore, we incorporated the V-G-dependency of the parasitic capacitance into the equivalent capacitance model, resulting in a more accurate extraction of g(DOS) (E). For validation, the proposed method was applied to amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs with an optical source with lambda=532 nm and obtained N-T = 6 x 10(15 )cm(-3)<middle dot>eV(-1),N-D= 7 x 10(13)cm(-3)<middle dot>eV(-1),kT(T )= 0.28 eV, and kT(D )= 0.7 eV of the exponential and gaussian superposed model of g(DOS)(E). The proposed method isexpected to be a useful tool in the characterization of AOSTFTs.