Unconventional cross sections in zinc phosphide nanowires grown using exclusively earth-abundant components

TL;DR

This study demonstrates the epitaxial growth of zinc phosphide nanowires with unconventional cross sections using only earth-abundant elements, revealing temperature-dependent morphologies and potential for sustainable solar energy applications.

Contribution

It introduces a method to grow Zn3P2 nanowires with novel cross sections using earth-abundant materials and elucidates the conditions influencing their morphology and twin structures.

Findings

Nanowires exhibit triangular, pseudo-pentagonal, and hexagonal cross sections depending on growth temperature.

Twin plane superlattice structures form at high temperatures and phosphine pressures, incorporating Sn.

The work paves the way for sustainable, earth-abundant nanowire-based solar energy devices.

Abstract

To enable lightweight and flexible solar cell applications it is imperative to develop direct bandgap absorber materials. Moreover, to enhance the potential sustainability impact of the technologies there is a drive to base the devices on earth-abundant and readily available elements. Herein, we report on the epitaxial growth of Zn3P2 nanowires using exclusively earth-abundant components, using Sn as the nanowire catalyst and Si (111) as the substrate. We observe that the nanowires exhibit a triangular cross section at lower temperatures, a pseudo-pentagonal cross section at intermediate temperatures, and a hexagonal cross section in a twin plane superlattice configuration at high temperatures and high V/II ratios. At low temperatures, the surface facets are constricted into a metastable configuration, yielding the triangular morphology due to the symmetry of the substrate, while intermediate temperatures facilitate the formation of a pseudo-pentagonal morphology with lower surface to volume ratio. The twin plane superlattice structure can only be observed at conditions that facilitate the incorporation of Sn into Zn3P2, which is needed to form heterotwins in the tetragonal structure, namely at high temperatures and high phosphine partial pressures. These findings show a clear pathway to use Zn3P2 nanowires in sustainable solar energy harvesting using exclusively earth-abundant components, as well as opening up a novel route of fabricating quantum wells inside nanowires using heterotwins.