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 SiO
₂
/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) = 10
¹⁰
-10
¹¹
cm
^-2
eV
^-1
over the bandgap.