Exceptionally High Carrier Mobility in Hexagonal Diamond

TL;DR

This study uses ab initio calculations to demonstrate that hexagonal diamond exhibits exceptionally high carrier mobility at room temperature, surpassing most known semiconductors due to unique scattering suppression mechanisms.

Contribution

The paper reveals the high carrier mobility in hexagonal diamond and uncovers two novel mechanisms responsible for this exceptional property.

Findings

Hole mobilities of 5631 and 5552 cm²V⁻¹s⁻¹ along xy and z directions

Electron mobilities of 11462 and 28464 cm²V⁻¹s⁻¹ along xy and z directions

Identification of two mechanisms: suppression of hole scattering and wavefunction decoupling.

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.