Surface conduction and reduced electrical resistivity in ultrathin noncrystalline NbP semimetal

TL;DR

This study reveals that ultrathin noncrystalline NbP semimetal films exhibit reduced electrical resistivity due to surface conduction, challenging conventional expectations of increased resistivity in thin metallic films and offering potential for nanoscale electronic applications.

Contribution

It demonstrates that noncrystalline NbP films show decreased resistivity with decreasing thickness, driven by surface conduction channels, unlike typical metals.

Findings

Resistivity decreases as NbP film thickness reduces below 5 nm.

Surface conduction channels dominate electrical transport in ultrathin NbP.

Resistivity in ultrathin NbP is lower than in conventional metals at similar thicknesses.

Abstract

The electrical resistivity of conventional metals, such as copper, is known to increase in thin films due to electron-surface scattering, limiting the performance of metals in nanoscale electronics. Here, we find an unusual reduction of resistivity with decreasing film thickness in niobium phosphide (NbP) semimetal deposited at relatively low temperatures of 400 \deg C. In films thinner than 5 nm, the room temperature resistivity (~34 microohm*cm for 1.5-nm-thick NbP) was up to six times lower than the bulk NbP resistivity, and lower than conventional metals at similar thickness (typically ~100 microohm*cm). Remarkably, the NbP films are not crystalline, but display local nanocrystalline, short-range order within an amorphous matrix. Our analysis suggests that the lower effective resistivity is due to conduction via surface channels, together with high surface carrier density and sufficiently good mobility as the film thickness is reduced. These results and the fundamental insights obtained here could enable ultrathin, low-resistivity wires for nanoelectronics, beyond the limitations of conventional metals.