Analysis of hysteresis behavior of pentacene field effect transistor characteristics with capacitance-voltage and optical second harmonic generation measurements

Abstract

Analyzing pentacene field effect transistors (FETs) with Au source and drain electrodes as Maxwell-Wagner effect elements, electron and hole injection from the Au electrodes into the FET channel were examined using capacitance-voltage (C−V) and optical second harmonic generation (SHG) measurements. The C−V characteristics show a hysteresis behavior that depends on gate-source (drain) stress biasing, Vgs(Vgd). Charge carriers forming the conducting channel of pentacene FET are mainly holes injected from Au electrodes. Results suggest that this hysteresis behavior is attributable to carriers trapped in the FET channel injected from the Au electrodes, and that hole injection is suppressed after Vgs<0 stress biasing, whereas it is assisted after Vgs>0. To further clarify the carrier injection mechanism for a different stress biasing condition, the modulation of the electric field along the FET channel by injected carriers was examined using SHG measurements. At the on state, the SHG signal was well diminished due to the hole injection from the Au electrodes, whereas the SHG was enhanced at the off state. However, interestingly, the enhanced SHG at the off state decayed gradually with a relaxation time of 103 s during the Vgs(=Vgd)=+100 V stress biasing. Results suggest that electron injection occurs from the Au source and drain electrodes into the pentacene and that they are subsequently trapped around Au electrodes. Based on these results, a mechanism of the hole injection assisted by trapped electrons in the pentacene is proposed for the C−V hysteresis behavior after stress-biasing Vgs>0.