Electronic Structure and Optical Properties of the Lonsdaleite Phase of Si, Ge and diamond

TL;DR

This study investigates the electronic and optical properties of diamond, silicon, and germanium in the lonsdaleite phase, revealing phase-dependent changes in their semiconductor behavior and optical anisotropy.

Contribution

It provides the first detailed calculations of the electronic structure and optical properties of these materials in the lonsdaleite phase using an empirical pseudopotential approach.

Findings

Diamond and Si remain indirect gap semiconductors in lonsdaleite phase.

Germanium becomes a direct gap semiconductor with a smaller band gap.

Strong polarization-dependent optical anisotropy is observed.

Abstract

Crystalline semiconductors may exist in different polytypic phases with significantly different electronic and optical properties. In this paper, we calculate the electronic structure and optical properties of diamond, Si and Ge in the lonsdaleite (hexagonal-diamond) phase. We use an empirical pseudopotentials method based on transferable model potentials, including spin-orbit interactions. We obtain band structures, densities of states and complex dielectric functions calculated in the dipole approximation for light polarized perpendicular and parallel to the c-axis of the crystal. We find strong polarization dependent optical anisotropy. Simple analytical expressions are provided for the dispersion relations. We find that in the lonsdaleite phase, diamond and Si remain indirect gap semiconductors while Ge is transformed into a direct gap semiconductor with a significantly smaller band gap.