Probing of channel formation in organic field effect transistors by optical second harmonic generation measurement

Abstract

Optical second harmonic generation (SHG) measurement was employed to compare the difference in carrier behavior between pentacene and copper(II)–phthalocyanine (CuPc) field-effect transistors (FETs). For pentacene FETs, SHG was enhanced in the off-state owing to Laplace electric field formation and it was diminished by carrier injection from the Au electrode. On the other hand, for CuPc, SHG was not enhanced in the off- and on-states. It was suggested that additional excess injected carriers exist even in the off-state for CuPc. A possible mechanism underlying the extinction of SHG in the off-state for CuPc was proposed.