Characterization of organic semiconductors by a large-signal capacitance-voltage method at high and low frequencies.

ITO/semiconductor/metal structures, with metal-free tetraphenylporphyrin (H2-TPP) as organic semiconductor, are investigated by means of a capacitance–voltage (C–V) method employing a large-signal triangular voltage waveform, which allows C–V measurements to be performed from 100 kHz to 100 mHz. The semiconductor layer, 60 nm in thickness, was deposited by molecular beam epitaxy on an ITO substrate and covered by aluminum back contacts. By performing the C–V measurements at low frequencies, transport and trapping of carriers are studied. On the contrary, when the signal frequencies are high in comparison with the carrier transit time in the device, metal–semiconductor interactions at the contacts are investigated.