The electrical resistivity of conventional metals such as copper is known to increase in thin films as a result of electron-surface scattering, thus 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°C. In films thinner than 5 nanometers, the room temperature resistivity (~34 microhm centimeters for 1.5-nanometer-thick NbP) is up to six times lower than the resistivity of our bulk NbP films, and lower than conventional metals at similar thickness (typically about 100 microhm centimeters). 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 caused by conduction through 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.
We dedicate this work in memory of the late Prof. A. K. M. Newaz (San Francisco State University) and Prof. E. Reed (Stanford University). We are grateful for discussions with them throughout the years and for their contribution to the scientific community. We also acknowledge Prof. H.-S. P. Wong for discussions and encouragement related to this work. A.I.K. is thankful to J. McVittie and C. Kline for their support and discussion regarding materials deposition, to S. Komera for the lab support, and to C. Lavoie for additional insights. The TEM work was supported by T. Cheon at the Daegu Gyeongbuk Institute of Science and Technology (DGIST). A.I.K. also thanks M. Noshin and H. Kwon for useful discussions on materials deposition. This work was performed at the Stanford Nanofabrication Facility (SNF) and Stanford Nano Shared Facilities (SNSF), which are supported by the National Science Foundation (NSF) award ECCS-2026822. The Stanford authors were supported in part by the Precourt Institute for Energy and the SystemX Alliance. A.I.K. acknowledges support from a Stanford Graduate Fellowship. E.L. and Y.S. were funded by the National Science Foundation (under grant no. 2037652). A.R. and F.H.J. acknowledge support from the NSF program Designing Materials to Revolutionize and Engineer our Future (DMREF project DMR-1922312). I.-K.O. acknowledges support from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIT grant RS-2024-00357895).
