Van der Pauw device for mobility measurement in organic semiconductors

Abstract

In this work, a Van der Pauw device was developed using photolithography to measure the carrier mobility of organic semiconductors. This device performs four-point measurements, minimizing the influence of contact resistance between the organic semiconductor and the metal contacts. Nickel contacts and SiO₂ gate dielectric were used. The device was fabricated on a Si wafer, which also serves as the device's gate. A thin layer of SiO₂ was created on the Si wafer before depositing the organic semiconductor, acting as the gate dielectric. The semiconductor used was Poly(3-hexylthiophene-2,5-diyl), which was deposited by spin coating. Theoretical modeling was performed using Van der Pauw theory along with a compact DC model for organic transistors. First-order approximations showed that by varying the gate voltage, the sheet conductance exhibited a linear dependence on the difference between the gate voltage and the average voltage of the measurement electrodes. Measurements were performed using a parameter analyzer, applying different gate voltages and current injections, with corresponding voltage values being measured. From the measured data, the values of sheet conductance and mobility were extracted. The mobility values obtained ranged from 0.1 to 0.5 cm²/(V.s), which are consistent with those reported in the literature using other methods. However, the results suggest that mobility values obtained by other methods may be underestimated due to the influence of contact resistance.