Brillouin – Mandelstam Spectroscopy of Acoustic Phonons in Boron-Doped Diamond – Implications for Thermal Management of Ultra-Wide-Band-Gap Electronics

We investigated bulk and surface acoustic phonons in the boron-doped single-crystal diamond films using the Brillouin-Mandelstam light scattering spectroscopy. It was found that the frequency and the group velocity of acoustic phonons decrease non-monotonically with the increasing boron doping concentration, revealing pronounced phonon softening. The change in the velocity of the shear horizontal acoustic phonons in the degenerately doped diamond was as large as ~15% as compared to the undoped diamond [1]. 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 concentrations but experienced a strong decrease at the high doping level. The obtained results have important implications for thermal transport in heavily doped diamond films used for ultra-wide-band-gap electronics. In evaluating the thermal conductivity of doped diamond films, one should take into consideration not only the concentration of dopants acting as scattering centers but also the changes in the acoustic phonon velocities.

[1] E. Guzman, et al. “Effects of boron doping on the bulk and surface acoustic phonons in single-crystal diamond", ACS Appl. Mater. Interfaces, 14, 37, 42223 (2022).