Noncontact potentiometry of polymer field-effect transistors

Abstract

We report on high-resolution potentiometry of operating organic thin-film field-effect transistors by means of scanning Kelvin probe force microscopy. It is demonstrated that the measured potential reflects the electrostatic potential of the accumulation layer at the semiconductor/insulator interface. We present data revealing gate bias and lateral electric field dependence of the field-effect mobility in poly(hexylthiophene) at temperatures from 50 to 300 K.

Direct observation of the charge carrier concentration in organic field-effect transistors by electron spin resonance

“…11 The surface potential profile of operating RR-P3HT FETs has been reported by using Kelvin probe force microscopy. 12 The observed potential profile has shown a clear change between the linear region ͑V gs Ͼ V ds ͒ and the saturation ͑or superlinear͒ region ͑V gs Ͻ V ds ͒ of the device, which may be consistent with the prediction of the standard FET theory in the first approximation. There have been, however, no direct observations of the change in the total charge carrier concentration in the operating FET channel region, corresponding to the change in the potential profile.…”

Probing stress effects in single crystal organic transistors by scanning Kelvin probe microscopy

“…© 2010 American Institute of Physics Scanning Kelvin probe microscopy (SKPM) has demonstrated utility in correlating the relationship between film structure and charge transport in organic thin-film transistor (OTFT) devices as well as providing a detailed view of charge injection at the source and drain contacts. [1][2][3][4][5][6][7] While traditional field effect transistor (FET) I-V (performance) measurements yield the average mobility of the device, SKPM offers the advantage of probing the local mobility of the device. Previous studies of rubrene single crystal (SC) OTFTs utilized SKPM data, specifically the slope of the potential profile in the device channel (V/µm), to directly calculate the intrinsic charge mobilities of individual devices (µ).…”

Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

“…The shape of such nonlinear potential profile has been experimentally observed by SKPM techniques. 18,19,[23][24][25] It is also noteworthy that the growth of the lateral electric field around the drain electrode at the pinch-off point has been observed by the second harmonic generation spectroscopy in the operating pentacene transistors. 48 In the saturation region of |V ds | > |V gs − V th |, the excess drain voltage is consumed in the narrow charge-depleted region around the drain electrode, and hence, there are no further changes of the potential shape or carrier concentration as well as the output current.…”

“…The shape of the potential profile has been experimentally observed in the operating OFET by using scanning Kelvin probe microscopy (SKPM), giving linear and superlinear distributions corresponding to the linear and the saturation regions of FET output characteristics, respectively. 18 The potential profile also gives detailed information of charge transport, such as contact resistance, [18][19][20][21] charge trapping at grain boundaries, [20][21][22] as well as charge concentration dependence of the mobility. [23][24][25] However, SKPM provides no spectroscopic information of charge carriers.…”