Extraction Technique for Intrinsic Subgap DOS in a-IGZO TFTs by De-Embedding the Parasitic Capacitance Through the Photonic $C$– $V$ Measurement

We report a technique for extraction of the intrinsic subgap density of states
$(g_{A, {\rm int}}(E))$
by deembedding the parasitic capacitance in amorphous indium–gallium–zinc–oxide TFTs through the optical charge pumping method. As structure-dependent parameters in the proposed extraction technique, the overlap length
$L_{\rm ov}$
between the source/drain (S/D) and the active layer and the parasitic overlap area between the gate and the S/D metal
$(C_{{\rm par}, S}/C_{{\rm par}, D})$
are considered under dark and subbandgap photonic states. We obtained
$g_{A, {\rm int}}(E)$
as a superposition of the exponential deep and tail states with
$N_{\rm TA, {\rm int}}\! =\! \hbox{6.0}\! \times\! \hbox{10}^{16}\ \hbox{eV}^{-1} \! \cdot\! \hbox{cm}^{-3}$
,
$kT_{\rm TA, {\rm int}}\! =\! \hbox{0.16}\ \hbox{eV}$
,
$N_{\rm DA, {\rm int}}\! =\break \hbox{1.8} \times \hbox{10}^{15}\ \hbox{eV}^{-1} \cdot \hbox{cm}^{-3}$
, and
$kT_{DA, {\rm int}} = \hbox{1.9}\ \hbox{eV}$
from samples with various parasitic areas.