Energy-level alignment and electrical properties of Al/p-type Si Schottky diodes with sorbitol-doped PEDOT:PSS as an organic interlayer

The current-voltage (I-V) characteristics of Al/p-type Si Schottky diodes with pristine and 5 wt.% sorbitol-doped organic PEDOT:PSS interlayers have been investigated. It was found that the barrier heights of the diodes with pristine and sorbitol-doped PEDOT:PSS are higher than those of a conventional Al/p-type Si Schottky diode because of the modification of the effective barrier height by the organic interlayer. It is noted that the Al/p-type Si Schottky diode with sorbitol-doped PEDOT:PSS interlayer exhibits higher barrier height and lower series resistance, as compared to Al/p-type Si Schottky diodes with pristine PEDOT:PSS interlayer. In addition, UPS measurements indicate that the position of the HOMO level is closer to the Fermi level for pristine PEDOT:PSS than for sorbitol-doped PEDOT:PSS. As a result, the hole injection barrier height is 0.15 eV lower in the pristine PEDOT:PSS structure than in the sorbitol-doped PEDOT:PSS. This value closely matches the difference in barrier heights (0.12 eV) seen in the I-V measurements. An energy-level alignment diagram is also presented and discussed for the structures studied. The Poole-Frenkel mechanism is found to dominate the reverse leakage current in both structures, indicating the presence of structural defects and trap levels in the organic film.