Fermi level pinning can determine polarity in semiconductor nanorods

TL;DR

This study demonstrates that Fermi level pinning at surface states critically influences the polarity of semiconductor nanorods, affecting their dipole moments, surface chemistry response, and size scaling.

Contribution

It reveals how Fermi level pinning at surface states determines nanorod polarity, a novel insight into surface electronic effects on nanostructure properties.

Findings

Fermi level coincides with surface states at nanorod ends

Surface states pin the potential difference across nanorods

Polarity depends on surface chemistry, size, and composition

Abstract

First-principles calculations of polar semiconductor nanorods reveal that their dipole moments are strongly influenced by Fermi level pinning. The Fermi level for an isolated nanorod is found to coincide with a significant density of electronic surface states at the end surfaces, which are either mid-gap states or band-edge states. These states pin the Fermi level, and therefore fix the potential difference across the rod. We provide evidence that this effect can have a determining influence on the polarity of nanorods, and has consequences for the way a rod responds to changes in its surface chemistry, the scaling of its dipole moment with its size, and the dependence of polarity on its composition.