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

Abstract

We report a technique for extraction of the intrinsic subgap density of states (gA,(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-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-par,C-S/C-par,C-D) are considered under dark and subbandgap photonic states. We obtained g(A,int)(E) as a superposition of the exponential deep and tail states with N-TA,N-int = 6.0x10(16) eV(-1) . cm(-3), kT(TA,int) = 0.16 eV, N-DA,N-int = 1.8 x 10(15) eV(-1) . cm(-3), and kT(DA,int) = 1.9 eV from samples with various parasitic areas.