Probing of the electric field distribution in organic field effect transistor channel by microscopic second-harmonic generation

Abstract

Electric field distribution in channel of pentacene field effect transistor (FET) was successfully probed by microscopic optical second-harmonic generation (SHG) observation. Microspot SHG signals were acquired at various points in the channel with scanning a spot position along source-drain direction. For the FET at off state, enhanced SHG signal was observed, indicating the Laplace field formation reflecting the device geometry. This clearly supports the insulating nature of pentacene layer at off state. After turning on the FET, SHG profile changed drastically, indicating change in the field distribution by the space charge formation in the channel due to the carrier injection.

Rearrangement of the molecular orientation of Alq3 in organic light-emitting diodes under constant current aging investigated using sum frequency generation spectroscopy

“…These phenomena are very similar to those observed in our previous EFI-SFG study of multi-layered OLEDs, and this behavior can be explained in terms of an electric field induced effect [9]. Thus, the SFG signal of ␣-NPD under the application of a forward voltage originates from the bulk of the ␣-NPD layer, as in the case of the EFI-SHG [24]. Note that no peaks derived from the ␣-NPD cation species are observed in the SFG spectra of the OLEDs due to the lack of the double-resonance effect, because the ␣-NPD cation species have no absorption around this wavelength.…”

Molecular structure and carrier distributions at semiconductor/dielectric interfaces in organic field-effect transistors studied with sum frequency generation microscopy

“…Second-harmonic-generation ͑SHG͒ microscopy is interface sensitive for materials with centrosymmetry 7 and has a better spatial resolution than IR microscopy. Manaka et al 8 have demonstrated that the SHG microscopy provides not only 2D mapping of electric field, but also carrier motion upon application of pulsed gate voltages. 9,10 In contrast to IR microscopy, however, this method does not provide any information of vibrational structure of molecules at the interfaces.…”

Probing motion of electric dipoles and carriers in organic monolayers by Maxwell Displacement Current and optical second harmonic generation

“…From Eqs. (3) and (4), it is clear that SH intensity distribution along the channel changes with change of the space charge field E s (x, t) [27][28][29], and thus with injected carrier distribution, ρ(x, t) (0b x b L). TRM-SHG measurement is based on this principle, and this approach allows nondestructive probing of a local electric field induced in materials because of the two-photon process, and also allows selective probing of a local electric field distribution in multi-layer systems in device applications such as OFET and organic electro-luminescent (EL) device by choosing laser wavelength appropriately.…”