| dc.description.abstract | This thesis investigates the application of a series of phosphonic acid self-assembled monolayers (PA SAMs) with different alkyl chain lengths to p-type organic semiconductors dinaphtho[2,3-b:2′,3 ′-f]thieno[3,2-b] (DNTT) as lateral and vertical transistors and DNTT combined with the inorganic semiconductor ZnO as ambipolar transistors to investigate the effect of PA SAMs on the structure and electrical properties of DNTT films by surface modification of metal oxide dielectric layers, electrodes, and inorganic semiconductors.
In the DNTT lateral transistors, the highest hole mobility of 3.9 cm2/Vs was found to be achieved by surface modification of the Al2O3 insulator layer with dodecyl PA SAM (C12), which is 6 times higher than Al2O3 without surface modification. In the DNTT vertical transistors, the highest hole mobility was found to be achieved if the perforated Au source electrode were modified with C12, and a similar trend was observed in the ZnO/DNTT ambipolar transistors in terms of electrical properties.
Further analyses of morphology, crystallinity and molecular orientation by Atomic Force Microscope (AFM), X-Ray Diffraction (XRD) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) confirm that deposition of DNTT on C12-modified Al2O3 forms larger grain structures and fewer grain boundaries, which is the main cause for the increased charge transport in both the lateral and vertical directions. In addition, UV photoelectron spectroscopy (UPS) measurements also show that modification of PA SAMs with longer alkyl chains in DNTT perforated Au source electrode slightly increases the injection barrier, but the effect on the transistor current is not significant.
In ZnO/DNTT ambipolar transistors, the C12-modified ZnO surface also contributes to improved DNTT hole mobility and reduced hysteresis, and represents a reduction in surface defect states.
Overall, we show that PA SAMs can be widely applied for surface modification of metal oxide dielectric materials, metals, and metal oxide semiconductors. Appropriate PA SAMs can effectively control the organic film structure deposited on top, thus enhancing the electrical performance of different device. | en_US |