Effect of isotope disorder on the Raman spectra of cubic boron arsenide

TL;DR

This study investigates how isotope disorder affects the Raman spectra of cubic boron arsenide, revealing insights into phonon behavior and disorder-activated scattering in isotopically varied crystals.

Contribution

It provides the first detailed Raman analysis of isotopically tailored c-BAs, highlighting effects of mass disorder and two-mode behavior in optical phonons.

Findings

Isotope disorder influences optical phonon modes.

Two-mode behavior observed in mixed crystals.

Disorder activates Raman scattering by acoustic phonons.

Abstract

Boron arsenide (c-BAs) is at the forefront of research on ultrahigh thermal conductivity materials. We present a Raman scattering study of isotopically tailored cubic boron arsenide single crystals for 11 isotopic compositions spanning the range from nearly pure c-$^{10}$BAs to nearly pure c-$^{11}$BAs. Our results provide insights on the effects of strong mass disorder on optical phonons and the appearance of two-mode behavior in the Raman spectra of mixed crystals. Strong isotope disorder also relaxes the one-phonon Raman selection rules, resulting in disorder-activated Raman scattering by acoustic phonons.