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Insights into the Interfacial Properties of Low-Voltage CuPc Field-Effect Transistor

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journal contribution
posted on 12.06.2013 by Yaorong Su, Ming Ouyang, Pengyi Liu, Zhi Luo, Weiguang Xie, Jianbin Xu
The interfacial transport properties and density of states (DOS) of CuPc near the dielectric surface in an operating organic field-effect transistor (OFET) are investigated using Kelvin probe force microscopy. We find that the carrier mobility of CuPc on high-k Al2Oy/TiOx (ATO) dielectrics under a channel electrical field of 4.3 × 102 V/cm reaches 20 times as large as that of CuPc on SiO2. The DOS of the highest occupied molecular orbital (HOMO) of CuPc on the ATO substrate has a Gaussian width of 0.33 ± 0.02 eV, and the traps DOS in the gap of CuPc on the ATO substrate is as small as 7 × 1017 cm–3. A gap state near the HOMO edge is observed and assigned to the doping level of oxygen. The measured HOMO DOS of CuPc on SiO2 decreases abruptly near EVGS = VT, and the pinning of DOS is observed, suggesting a higher trap DOS of 1019–1020 cm–3 at the interface. The relationships between DOS and the structural, chemical, as well as electrical properties at the interface are discussed. The superior performance of CuPc/ATO OFET is attributed to the low trap DOS and doping effect.