Crystalline Field Effect Transistors Research Articles

(BEDT-TTF)(TCNQ)結晶FETの電界効果移動度にみられる多段階相転移(発光・表示記録用有機材料およびデバイス・一般)

(BEDT-TTF)(TCNQ)結晶FETの電界効果移動度にみられる多段階相転移(発光・表示記録用有機材料およびデバイス・一般)

Gate-Induced Thermally Stimulated Current on the Ferroelectric-like Dielectric Properties of (BEDT-TTF)(TCNQ) Crystalline Field Effect Transistor

A gate-induced thermally stimulated current (TSC) on β′-(BEDT-TTF)(TCNQ) crystalline FET were conducted to elucidate the previously observed ferroelectric-like behaviors. TSC which is symmetric for the polarization of an applied VPG and has a peak at around 285 K was assigned as a pyroelectric current. By integrating the pyroelectric current, temperature dependence of the remnant polarization charge was obtained and the existence of the ferroelectric phase transition at 285 K was clearly demonstrated. We have tentatively concluded that the phase transition between dimer Mott insulator and charge ordered phase occurred at around the interface of organic crystal and substrate.

Dependence of mobility on shallow localized gap states in single-crystal organic field-effect-transistors

Abstract In order to optimize the performance of molecular organic electronic devices it is important to study the intermolecular density of states and charge transport mechanisms in the environment of crystalline organic material. Using this approach in Field Effect Transistors (FETs) we show that material purification improves carrier mobility and decreases density of the deep localized electronic state. We also report a general exponential energy dependence of the density of localized states in a vicinity of the mobility edge (Fermi energies up to ∼7 times higher than the thermal energy ( kT )) in a variety of the extensively purified molecular organic crystal FETs. This observation and the low activation energy of the order of ∼ kT suggest that molecular structural misplacements of the sizes that are comparable with thermal molecular modes rather than impurity deep traps play a role in formation of these shallow states. We find that the charge carrier mobility in the FET nanochannels, μ eff , is parameterized by two factors, the free-carrier mobility, μ 0 , and the ratio of the free carrier density to the total carrier density induced by gate bias. Crystalline FETs fabricated from rubrene, pentacene, and tetracene have a high free-carrier mobility, μ 0 ∼50 cm 2 /Vs, at 300 K with lower device μ eff dominated by localized shallow gap states. This relationship suggests that further improvements in electronic performance could be possible with enhanced device quality.