Exceptionally High Carrier Mobility in Hexagonal Diamond

Hexagonal diamond (h-diamond), or Lonsdaleite, has been reported to be a wide-bandgap semiconductor with high thermal conductivity and hardness. Our $\mathit{\text{ab}}\mathit{\text{initio}}$ calculations reveal its exceptionally high carrier mobility at room temperature. Along $xy$ and $z$ directions, the hole mobilities are 5631 and 5552 cm${}^2$V${}^{-1}$s${}^{-1}$, and the electron mobilities are 11462 and 28464 cm${}^2$V${}^{-1}$s${}^{-1}$, respectively. These values are significantly superior to the mobility of most known semiconductors including cubic diamond. The small effective masses in h-diamond, comparable to those in cubic diamond, cannot explain its substantially higher mobility. Instead, two crucial mechanisms are uncovered: selection rules that considerably suppress hole scattering induced by transverse acoustic phonons, and a spatial decoupling effect where electronic wavefunctions concentrated in lattice interstitials lead to minimal overlap with scattering potentials.