Sub-Bandgap Photonic Capacitance-Voltage Method for Characterization of the Interface Traps in Low Temperature Poly-Silicon Thin-Film Transistors

Abstract

Sub-bandgap (E-ph < E-g) photonic capacitancevoltage method (PCVM) is proposed for the energy distribution [D-it(E)] of interface traps at the SiO2/low temperature poly-silicon (LTPS) junction interface in LTPS thin-film transistors (TFTs). The differential capacitance-voltage (C-V) characteristics under dark and sub-bandgap photoillumination are obtained by excitation of electrons from the valence band to the empty interface states over the photoresponsive range (E-F <= E-t <= E-V + E-ph) while suppressing the band-to-band electron-hole-pair generation. We applied the sub-bandgap PCVM technique to accumulation mode p-channel LTPS TFTs with W/L = 3/30 mu m/mu m. Extracted interface trap density ranges D-it(E) = 10(10)-10(11) cm(-2)eV(-1) over the bandgap.