Semiconducting character of LaN: magnitude of the band gap, and origin of the electrical conductivity

TL;DR

This study uses hybrid density functional theory to establish that LaN is a direct-band-gap semiconductor with a 0.62 eV gap, and identifies nitrogen vacancies and oxygen substitutions as sources of its electrical conductivity.

Contribution

The paper provides the first conclusive computational evidence that LaN is a semiconductor and identifies defect types responsible for its conductivity, clarifying previous uncertainties.

Findings

LaN is a direct-band-gap semiconductor with a 0.62 eV gap.

Nitrogen vacancies and oxygen substitutions act as shallow donors.

Light effective masses suggest potential for electronic applications.

Abstract

Lanthanum nitride (LaN) has attracted research interest in catalysis due to its ability to activate the triple bonds of N$_2$ molecules, enabling efficient and cost-effective synthesis of ammonia from N$_2$ gas. While exciting progress has been made to use LaN in functional applications, the electronic character of LaN (metallic, semi-metallic, or semiconducting) and magnitude of its band gap have so far not been conclusively determined. Here, we investigate the electronic properties of LaN with hybrid density functional theory calculations. In contrast to previous claims that LaN is semi-metallic, our calculations show that LaN is a direct-band-gap semiconductor with a band-gap value of 0.62 eV at the X point of the Brillouin zone. The dispersive character of the bands near the band edges leads to light electron and hole effective masses, making LaN promising for electronic and optoelectronic applications. Our calculations also reveal that nitrogen vacancies and substitutional oxygen atoms are two unintentional shallow donors with low formation energies that can explain the origin of the previously reported electrical conductivity. Our calculations clarify the semiconducting nature of LaN and reveal candidate unintentional point defects that are likely responsible for its measured electrical conductivity.