Exceptionally High Carrier Mobility in Hexagonal Diamond

Abstract

Hexagonal diamond (h-diamond), or Lonsdaleite, has been reported to be a wide-bandgap semiconductor with high thermal conductivity and hardness. Our \textit{ab 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.