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, 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 lengthLₒᵥbetween the source/drain (S/D) and the active layer and the parasitic overlap area between the gate and the S/D metal(C_ par, S/C_ par, D)are considered under dark and subbandgap photonic states. We obtainedg_A, int(E)as a superposition of the exponential deep and tail states withN_ TA, int\! =\! 6.0\! ×\! 10¹⁶\ eV⁻¹ \! ·\! cm⁻³,kT_ TA, int\! =\! 0.16\ eV,N_ DA, int\! = 1.8 × 10¹⁵\ eV⁻¹ · cm⁻³, andkT_DA, int = 1.9\ eVfrom samples with various parasitic areas.