Interface Engineering for Organic Electronics; Manufacturing of Hybrid Inorganic-Organic Molecular Crystal Devices
Prof. dr. ing. A.J.H.M. Rijnders
Prof. dr. ing. D.H.A. Blank
Organic semiconductors are at the basis of Organic Electronics. Objective of this dissertation is “to fabricate high-quality organic molecular single-crystal devices”, to explore the intrinsic properties of organic semiconductors. To achieve this, the in situ fabrication of complete field-effect transistors by direct deposition of metal contacts and oxide gate dielectrics on the surface of free-standing pentacene single-crystals at room temperature (with the ‘quasi-dynamic stencil deposition’ technique in pulsed laser deposition) is selected as main approach. First, the structure of vapor-grown pentacene single-crystals is investigated. The observed morphology shows step flow is the dominant crystal growth mechanism. For pentacene, the most common oxidation product and largest impurity present is 6,13-pentacenequinone. It is observed that this quinone is preferentially located as a thin monolayer (partly) covering the crystal surface. In order to remove the quinones selectively, the partly-oxidized crystals are heated in vacuum at a fixed temperature overnight. Next, the direct deposition of various materials through a stencil on the pentacene singlecrystal surface by PLD is investigated. By taking several precautions in the process, lowkinetic energy deposition or ‘soft-landing’ was achieved. Smooth and isolated patterns with a well-defined geometry were successfully deposited, without obvious destruction of the fragile substrate. The terraced structure of the underlying pentacene substrate is often still noticeable on top of the patterned features. A series of gold patterns is deposited on silicon oxide and pentacene single-crystals; the results show that the growth evolution of the surface roughness is similar on both kinds of substrates. Finally, the influence of the deposition parameters applied in the device fabrication and performing a heat treatment on the electrical properties of pentacene single-crystals is investigated, by characterizing space-charge-limited current and field-effect transistor devices fabricated on the surface of pentacene single-crystals.