In-Crystal and Surface Charge Transport of Electric-Field-Induced Carriers in Organic Single-Crystal Semiconductors

Abstract

Gate-voltage dependence of carrier mobility is measured in high-performance field-effect transistors of rubrene single crystals by simultaneous detection of the longitudinal conductivity sigma(square) and Hall coefficient R(H). The Hall mobility mu(H) (identical with sigma(square)R(H)) reaches nearly 10 cm(2)/V s when relatively low-density carriers (<10(11) cm(-2)) distribute into the crystal. mu(H) rapidly decreases with higher-density carriers as they are essentially confined to the surface and are subjected to randomness of the amorphous gate insulators. The mechanism to realize high carrier mobility in the organic transistor devices involves intrinsic-semiconductor character of the high-purity organic crystals and diffusive bandlike carrier transport in the bulk.

Hopping transport and the Hall effect near the insulator–metal transition in electrochemically gated poly(3-hexylthiophene) transistors

“…Electrostatic gating in the field-effect transistor geometry is ideal for such studies, as it enables wide-range tuning of the carrier density in a single sample 16 . A clear crossover to band transport has indeed been detected in such devices, via observation of a phonon-limited temperature dependence of the mobility, a robust Hall effect, and equivalence of the Hall mobility and the mobility extracted from gate voltagedependent measurements 14,15 . Semiconducting polymers, perhaps unsurprisingly given their lower crystallinity, low bandwidth and greater disorder, lag somewhat behind.…”

Charge-transfer induced surface conductivity for a copper based inorganic-organic hybrid

“…First, FETs were fabricated either by laminating the crystal onto prefabricated doped silicon with a silicon dioxide dielectric or by evaporating dielectric parylene films on top of the crystals. [11][12][13] Second, a layer of electrically insulating, electron donating TTF ͑600 nm thick͒ was evaporated on top of the crystal. In this case gold contacts were used to prevent re-evaporation of the TTF-TCNQ.…”

The emergence of charge coherence in soft molecular organic semiconductors via the suppression of thermal fluctuations

“…Therefore, the wavefunction must be coherent over several molecules. [3][4][5] For these reasons, the experimental observation of the Hall effect in the hopping systems of localized charge carriers significantly differs from that of band-transport systems. More precisely, the inverse Hall coefficient 1/R H equals the charge density Q only if the charge carriers are coherent.…”

“…According to definition, αo1 represents the situation where the electronic system cannot be described by fully coherent wavefunctions, while α = 1 represents systems with fully coherent charge transport as is observed in high-mobility organic semiconductors, such as rubrene, DNTT, alkyl-DNTT and pentacene derivatives. [4][5][12][13][14] We note that the effect of inelastic scattering is minor in organic semiconductors, so that α41 is unlikely.…”

“…6 A similar observation has been reported for organic polymers: if they are dominated by static disorder, then they only show a weak Hall signal, 7 whereas, in more ordered polymers, a free-electron-like wavefunction has been measured. 8 In previous studies, we successfully measured the Hall effect in organic semiconductors using rubrene single-crystal transistors, 3,5 which are well known to be the highest performing organic transistors at room temperature, with a mobility above 20 cm 2 Vs − 1 . [9][10][11] The experiment showed precise measurements for the band-transport relation, that is, R H = 1/Q, indicating coherent electronic states.…”