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- Small signal analysis of MPCVD diamond Schottky diodesPublication . Mendes, J. C.; L, Gomes H; Trippe, S. C.; Mukherjee, D.; Pereira, L.Polycrystalline diamond (PCD) grown by chemical vapor deposition (CVD) is an intrinsic semiconductor particularly attractive for high power/high temperature devices. Nevertheless, the physical models for injection and transport of electrical carriers are remarkable complex and depend on the microstructure and composition of carbon species in the film. In this work, free-standing CVD PCD films were deposited by microwave plasma CVD (MPCVD) and were characterized by Raman spectroscopy. Gold and aluminum circular contacts were deposited on the growth surface in order to fabricate a planar diode. The current-voltage characteristics were measured at different temperatures. The application of a non-homogeneous barrier model to fit the current-voltage characteristics reveals the existence of two barriers related with the grain/electrode and grain boundary/electrode interfaces. Small signal analysis was performed at room temperature to understand the nature of electrical process involved in the injection and carrier transport. The existence of parallel channels through with charge flows was confirmed and the fittings suggest the existence of a nearly equipotential surface at the interface diamond/electrode. The physical origin of the inclusion of a constant phase element in the equivalent circuit model is discussed. The results obtained are of particular importance to further devices fabrication. Prime novelty: An equivalent circuit model for the diamond Schottky diode is proposed
- The role of the electrode configuration on the electrical properties of small-molecule semiconductor thin-filmsPublication . Merces, Leandro; de Oliveira, Rafael Furlan; Gomes, Henrique L.; Bof Bufon, Carlos CesarThis paper presents a systematic analysis of the electrode configuration influence on the electrical properties of organic semiconductor (OSC) thin-film devices. We have fabricated and electrically characterized a set of planar two-terminal devices. The differences in I-V characteristics between the top and bottom contact structures are presented and analyzed. Top-contact configurations have a linear current vs. electric field behavior, while the bottom-electrode devices display a transition from ohmic to spacecharge-limited conduction regime. The transition is temperature-and thickness-dependent. Finite-element calculations show that when the OSC film is connected using top electrodes, the current flows through the OSC bulk region. On the other hand, the bottom-electrode configuration allows most of the current to flow near the OSC/substrate interface. The current probes interfacial states resulting in a space-charge conduction regime. The results shed some light on the so-called "contact effects" commonly observed in organic thin-film transistors. The findings presented here have implications for both the understanding of the charge transport in OSC films and the design of organic semiconductor devices. (C) 2017 Elsevier B.V. All rights reserved.