C₆₀thin-film transistors with high field-effect mobility, fabricated by molecular beam deposition

Abstract

We report performance of C 60 thin-film field-effect transistors and characterizations of C 60 thin-films on SiO 2 substrates fabricated by molecular beam deposition. Devices, fabricated and characterized under high vacuum without exposing to air, routinely showed current on/off ratios .10 8 and field-effect mobility in the range of 0.5-0.3 cm 2 /V s. The obtained mobility is comparable to the highest value among n-type organic thin-film transistors and close to that derived from the photocurrent measurements on C 60 thin-films. The grain size of C 60 thin-film, condensed in an fcc solid, increases with the substrate temperature, while the mobility did not exhibit a clear relation with substrate temperature. q

Electronic transitions and band offsets in C60:SubPc and C60:MgPc on MoO3 studied by modulated surface photovoltage spectroscopy

“…32 At first glance, the time at which the SPV signal reached its maximum can be related to the dielectric relaxation time 33 depending on the reciprocal conductivity and therefore on the reciprocal electron mobility. The mobility of electrons in C 60 layers, for example, is about 0.5-1.0 cm 2 /V s in the case of sublimed and molecular beam deposited films 18,34 and up to 5 cm 2 /V s in the case of deposition onto molecular-wetting controlled substrates. 35 In contrast, the electron mobility in metal phthalocyanine (MPc) layers is by 3-4 orders of magnitude lower in comparison to C 60 layers.…”

Analysis of carrier behavior in C60/P(VDF-TrFE) double-layer capacitor by using electric-field-induced optical second-harmonic generation measurement

“…36, two kinds of electron traps in C60 film were reported, i.e., deep electron traps of 0.37-0.42 eV positioned below a lowest unoccupied molecular orbital (LUMO) level, and shallow electron traps of 0.22-0.23 eV. The former ones are attributed to the roughness of interface contact (C60/P(VDF-TrFE) and C60/Au interfaces) and grain boundaries among crystallites in C60 film, 14 while the latter ones originate from the absorbed oxygen or water molecules. [33][34][35][36] In our preparation process of capacitors, thermal evaporated C60 film was transferred to another chamber for evaporating Au (Al) electrode.…”

“…Fullerene C60 has been known as a typical electron transfer material, a so-called n-type semiconductor, with high electron mobility (>0.1 cm 2 /V Á s), [14][15][16][17][18] and thus widely used in OFETs, [14][15][16][17][18] OLEDs, [19][20][21] and OPVs. [22][23][24] Studying carrier behaviors in the C60 devices using P(VDF-TrFE) will be quite instructive, to further extend our knowledge for the use of internal electric field induced by the spontaneous polarization of ferroelectric P(VDF-TrFE) layer in organic devices.…”

Thin-film fullerenes for organic field-effect transistors and complementary digital logic circuits

“…Compared to Haddon's C 60 OFETs, these devices also exhibited higher threshold voltages (27 V compared to 15 V) and on-off current ratios that were one order of magnitude lower (10 5 compared to 10 6 ). Because n-type organic semiconductors are susceptible to the effects of oxygen, 8 devices exhibiting the highest mobility values 4,5,6,7 have been both fabricated and tested under ultra-high vacuum (UHV) conditions. One report of stable operation of C 60 OFETs in air used an Ar sputtered, low oxygen content alumina (Al 2 O 3 ) passivation layer that resulted in no degradation in transistor performance for more than one month but the mobility was only 0.1 cm 2 /Vs.…”