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.