Assessment of the notions of band offsets, wells and barriers at nanoscale semiconductor heterojunctions

TL;DR

This paper reveals that at the nanoscale, semiconductor heterostructures exhibit complex potential behaviors beyond simple interface steps, impacting the design of nanoscale electronic devices.

Contribution

It demonstrates through self-consistent tight-binding calculations that nanoscale heterostructures can have non-uniform potential profiles, challenging traditional assumptions.

Findings

Potential varies significantly away from interfaces in nanoscale heterostructures.

Shell capping influences the potential landscape.

New strategies for electronic property engineering at the nanoscale.

Abstract

Epitaxially-grown semiconductor heterostructures give the possibility to tailor the potential landscape for the carriers in a very controlled way. In planar lattice-matched heterostructures, the potential has indeed a very simple and easily predictable behavior: it is constant everywhere except at the interfaces where there is a step (discontinuity) which only depends on the composition of the semiconductors in contact. In this paper, we show that this universally accepted picture can be invalid in nanoscale heterostructures (e.g., quantum dots, rods, nanowires) which can be presently fabricated in a large variety of forms. Self-consistent tight-binding calculations applied to systems containing up to 75 000 atoms indeed demonstrate that the potential may have a more complex behavior in axial hetero-nanostructures: The band edges can show significant variations far from the interfaces if the nanostructures are not capped with a homogeneous shell. These results suggest new strategies to engineer the electronic properties of nanoscale objects, e.g. for sensors and photovoltaics.