Electronic and structural properties of rare-earth mono-pnictide (RE-V) nanoparticles in III-V matrices

Embedding semi-metallic rare-earth mono-pnictide (RE-V) nanoparticles into III-V semiconductors enables nanocomposites with a wide range of optical, electrical, and thermoelectric properties. The inclusion of nanostructured components in a III-V increases the area of interfaces contributing to decreased carrier lifetime, increased phonon scattering, and reduced thermal conductivity, also providing enhanced electrical conduction through electron filtering mechanisms. The common group-V sublattice offers an interesting matching across interfaces of the rock-salt semimetal RE-V (e.g. ErAs) to the zinc-blende semiconductor III-V (e.g. GaAs, AlAs) matrices with similar lattice parameters. First-principles calculations based on density functional theory (DFT) calculation with the modified Becke-Johnson meta-GGA (mBJ) functional are used to describe the electronic properties of ErAs nanoparticles embedded in GaAs and AlAs. We investigate the stability of different nanoparticle shapes and sizes, from cubic to spherical, deriving a direct correlation between the electron density and atomic density associated with excess metal atoms at the interface. We find that spherical nanoparticles lead to lower atomic density at the interface and low formation enthalpies; the shape, size, and structure of the nanoparticles show good agreement with images obtained from transmission electron microscopy. Comparison of atom-resolved density of states (DOS) for different size and shaped nanoparticles with the parent compound materials allows for alignment the Fermi level of the nanoparticle systems with band edges of the semiconductors, showing that the Fermi level is pinned in the band gap. Our results show that as the size of ErAs nanoparticles increases, the Fermi level moves from near the conduction band for very small particles to the middle of the gap. Our predictions serve to guide the design of nanocomposite materials with targeted properties.