Fabrication of organic tunnel diodes with ultra-thin TiO2 interfacial layers
Heinonen, Pasi Petteri
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Organic tunnel diodes that exhibit negative differential resistance (NDR) at room temperature offer novel opportunities for organic logic circuits. Reproducible, room temperature NDR has been shown for organic devices with ultra-thin titanium dioxide layers incorporated into conventional Schottky diode structures. For industrial applications, the device fabrication process should be suitable for high-throughput processes. The specific issue is the fabrication of the oxide layers. In this work, two methods to fabricate the oxide layers were utilized: anodic oxidation and atomic layer deposition. The objective was to successfully fabricate and characterize the oxide layers and to fabricate organic tunnel diode devices. Vertical ITO/TiO2/semiconductor/aluminum -device structures were fabricated. The oxide layers were analyzed with x-ray photoelectron spectroscopy and Mott Schottky analysis. Current-voltage (I-V) measurements were performed for the devices. TiO2 layers of different thicknesses with high defect density as required for the tunneling process were successfully fabricated with the anodic oxidation method. The dielectric constant and defect density were 18 and 5×1019 cm-3, respectively, for the anodized layers. Fabricated devices with anodic oxidation and ALD grown oxide layers showed an N-shaped I-V characteristic with room temperature NDR. Observed peak-to-valley current ratio was over 3, which is enough for some novel logic circuits.