Disappearing of the Fermi level pinning at semiconductor interfaces

TL;DR

This paper reveals a universal behavior of Fermi level shifts at semiconductor interfaces, showing that the Fermi level position depends on film thickness and substrate work function, unifying various experimental observations.

Contribution

It introduces a universal analytical model explaining Fermi level pinning disappearance across diverse semiconductor interfaces, bridging experimental discrepancies.

Findings

Fermi level position depends on film thickness and substrate work function.

Disappearance of Fermi level pinning occurs at a critical film thickness.

Unified understanding of Fermi level behavior in inorganic, organic, and hybrid semiconductors.

Abstract

We identify a universality in the Fermi level change of Van der Waals interacting semiconductor interfaces-based Schottky junctions. We show that the disappearing of quasi-Fermi level pinning at a certain thickness of semiconductor films for both intrinsic (undoped) and extrinsic (doped) semiconductors, over a wide range of bulk systems including inorganic, organic, and even organic-inorganic hybridized semiconductors. The Fermi level (EF) position located in the energy bandgap was dominated by not only the substrate work function, but also the thickness of semiconductor films, in which the final EF shall be located at the position reflecting the thermal equilibrium of semiconductors themselves. Such universalities originate from the charge transfer between the substrate and semiconductor films after solving one-dimensional Poisson's equation. Our calculation resolves some of the conflicting results from experimental results determined by using ultraviolet photoelectron spectroscopy (UPS) and unifies the general rule on extracting EF positions in energy bandgaps from (i) inorganic semiconductors to organic semiconductors and (ii) intrinsic (undoped) to extrinsic (doped) semiconductors. Our findings shall provide a simple analytical scaling for obtaining the quantitative energy diagram regarding thickness in the real devices, thus paving the way for a fundamental understanding of interface physics and designing functional devices.