Extraction Technique for the Conduction Band Minimum Energy in Amorphous Indium–Gallium–Zinc–Oxide Thin Film Transistors

The conduction band minimum energy in amorphous oxide semiconductor-based thin film transistors (AOS TFTs) is a key parameter governing the accurate extraction of energy distribution for the subgap density-of-states (DOSs) and carrier mobility. We report a technique for extraction of the gate voltage ( ${V}_{\text {CBM}}{)}$ and corresponding energy ( ${E}_{\text {F},{\text {CBM}}}$ = ${E}_{\text {C}-{\text {EREF}}}{)}$ for the quasi-Fermi level ( ${E}_{\text {F}}{)}$ equal to the conduction band minimum ( ${E}_{\text {C}}{)}$ as ${V}_{\text {CBM}}$ = ${V}_{\text {GS}}$ ( ${E}_{\text {F}}$ = ${E}_{\text {C}}{)}$ and ${E}_{\text {F},{\text {CBM}}}$ = ${E}_{\text {F}}$ ( ${V}_{\text {GS}}$ = ${V}_{\text {CBM}}{)}$ . In order to confirm this technique through optoelectronic experimental data, amorphous indium–gallium–zinc–oxide (a-IGZO)-based thin film transistor was irradiated with various wavelengths and power, and obtained ${V}_{\text {CBM}}$ = 7.1 V and ${E}_{\text {F} {\text {CBM}}}$ = 71 meV in the dark state. This technique is expected to be useful in the accurate characterization of the subgap DOS and the effective mobility in AOS TFTs through a simple and effective extraction process.