Modified Conductance Method for Extraction of Subgap Density of States in a-IGZO Thin-Film Transistors

摘要

We propose a modified conductance method for extraction of the subgap density of states (DOS) in amorphous indium–gallium–zinc oxide thin-film transistors by using the measured capacitance and conductance through the capacitance–voltage ($C$– $V$) measurement. In the proposed method, the subgap DOS [ $g_{A}(E)$] is extracted from the frequency-dispersive $C$–$V$ characteristics by localized traps in the active channel region. The extracted $g_{A}(E)$ shows a superposition of the exponential tail states and the exponential deep states over the bandgap ($N_{rm TA} = hbox{3} times hbox{10}^{18} hbox{cm}^{-3} cdot hbox{eV}^{-1}$, $N_{rm DA} = hbox{2.8} times hbox{10}^{17} hbox{cm}^{-3} cdot hbox{eV}^{-1}$, $kT_{rm TA} = hbox{0.04} hbox{eV}$, and $kT_{rm DA} = hbox{0.77} hbox{eV}$ ). We note that the gate-bias-dependent $C_{rm free}$ by free electron charges can be separated from $C_{rm loc}$ by localized trap charges through the proposed method.