Extraction of Density of States in Amorphous GaInZnO Thin-Film Transistors by Combining an Optical Charge Pumping and Capacitance–Voltage Characteristics

A technique for extracting the acceptorlike density of states (DOS) of <i>n</i>-channel amorphous GaInZnO (a-GIZO) thin-film transistors based on the combination of subbandgap optical charge pumping and <i>C</i>-<i>V</i> characteristics is proposed. While the energy level is scanned by the photon energy and the gate voltage sweep, its density is extracted from the optical response of <i>C</i>-<i>V</i> characteristics. The extracted DOS shows the superposition of the exponential tail states and the Gaussian deep states (<i>N</i> _TA=2times10¹⁸ eV^-1ldrcm^-3, <i>N</i> _DA=4times10¹⁵ eV^-1ldrcm^-3, <i>kT</i> _TA=0.085 eV, <i>kT</i> _DA=0.5 eV , <i>E</i> _O=1 eV). The TCAD simulation results incorporated by the extracted DOS show good agreements with the measured transfer and output characteristics of a-GIZO thin-film transistors with a single set of process-controlled parameters.