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

• Modification of barrier height of Al/p-Si Schottky diode by PEDOT:PSS interlayer.
• Sorbitol-doped PEDOT:PSS interlayer shows lower series resistance than pristine one.
• Lower hole barrier height of pristine PEDOT:PSS, compared to sorbitol-doped one.
• Presence of structural defects and trap levels in the PEDOT:PSS 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.