Soumya Dutta

In this paper, we present the operation principle of an organic metal-insulator-semiconductor (MIS) capacitor where the organic semiconductor is undoped. In spite of a low charge concentration within the semiconductor, this device exhibits a capacitance variation with respect to the applied gate voltage yielding the capacitance-voltage characteristics similar to that of a traditional MIS capacitor based on the doped semiconductor. A physics-based model is developed to derive the charge concentration, surface potential, and the capacitance of the organic MIS capacitor. The model is validated with TCAD simulation results as well as with experimental data obtained from the fabricated organic MIS capacitor consisting of poly(4-vinylphenol) and poly(3-hexylthiophene-2, 5-diyl) as an insulator and a semiconductor, respectively.

Whether organic semiconductors, in their pristine form, are inherently intrinsic or involuntarily doped is an open question that is yet to be addressed. In this work, the source of charge carriers within pristine organic semiconductors, processed in a controlled inert ambience, is investigated using organic metal–insulator–metal capacitor (OMISCAP) devices. Top-gate and bottom-gate architecture of OMISCAP devices based on various organic semiconductors along with different combinations of metal–semiconductor junctions are demonstrated. The impact of the metal–semiconductor junction and the semiconductor thickness on the capacitance–voltage (C–V) characteristics of MISCAP devices is studied to ensure the role of contact-induced charge injection into the semiconductor, contrary to involuntary doping as the source of charge. The charge injection from the metal to the semiconductor is found to be the predominant source of charge carriers inside a pristine organic semiconductor rather than inadvertent doping. The findings in this report are further substantiated using TCAD device simulation.