We
report the results of the investigation of bulk and surface
acoustic phonons in the undoped and boron-doped single-crystal diamond
films using the Brillouin–Mandelstam light scattering spectroscopy.
The evolution of the optical phonons in the same set of samples was
monitored with Raman spectroscopy. It was found that the frequency
and the group velocity of acoustic phonons decrease nonmonotonically
with the increasing boron doping concentration, revealing pronounced
phonon softening. The change in the velocity of the shear-horizontal
and the high-frequency pseudo-longitudinal acoustic phonons in the
degenerately doped diamond, as compared to that in the undoped diamond,
was as large as ∼15% and ∼12%, respectively. As a result
of boron doping, the velocity of the bulk longitudinal and transverse
acoustic phonons decreased correspondingly. The frequency of the optical
phonons was unaffected at low boron concentration but experienced
a strong decrease at the high doping level. The density-functional-theory
calculations of the phonon band structure for the pristine and highly
doped samples confirm the phonon softening as a result of boron doping
in diamond. The obtained results have important implications for thermal
transport in heavily doped diamond, which is a promising material
for ultra-wide-band-gap electronics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.