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

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 μm/μm. Extracted interface trap density ranges D_it(E) = 10¹⁰-10¹¹ cm^-2eV^-1 over the bandgap.