Semiconducting character of LaN: Magnitude of the bandgap and origin of the electrical conductivity

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.Nitride compounds are a rich class of functional materials. The main-group III-nitrides are important semiconductors that find applications in electronics, optoelectronics, and photocatalysis.Recently, transition-metal and rare-earth nitrides have attracted attention due to their promise in, e.g., piezoelectric, 1 superconducting, 2 and catalysis applications. 3,4 In particular, Ye et al.discovered that lanthanum nitride (LaN) facilitates stable and highly efficient ammonia synthesis through the activation of N2 gas by nitrogen vacancies at the surface. LaN shows a catalytic

Pressure driven structural phase transitions and modulations in optical properties of lanthanum nitride: an account from on the fly molecular dynamics and SCF vis-à-vis non-SCF first-principle calculations

“…From figure 7(A, a) and table S1, it is clearly seen that both SCF as well as the nSCF calculations at PBE+U+ SOC, PBESOL + U + SOC, PW91 + U + SOC, TB09 + U + SOC and HSE06 + U + SOC level of theories underestimate the experimental band gap (E g ∼ 0.82 eV) reported elsewhere [57]. In this connection it may be relevant to mention that although Yan et al reported E g ∼ 0.82 respectively for the compound with HSE06 functional in complete agreement with the experimental observation, however our calculations with the same functional (HSE06) estimate Eg to be ∼0.60 , 0.62 eV for both SCF ,nSCF approaches in line with the existing literature [59]. Interestingly in our case E g ∼ 0.804 (0.80) eV, has been estimated from B3LYP + U + SOC level of theory for SCF (nSCF) calculations.…”

“…In fact much closer value of E g with the experimental observations had also been reported from the first-principle calculations using HSE functional (E g = 0.82 eV) [58]. However, even with simple inclusion of range separation parameter 'ω = 0.11 Bohr −1 ', HSE06, HSE06 + GW and HSE06 + spin-orbit coupling (SOC) levels of theory although predict direct band gaps with E g = 0.75, 0.68 and 0.62 eV respectively, but their estimated values are well deviated from the experimental observations [59]. The results from the first-principle calculations thus indicate the sensitivity of the HSE functional with 'ω' in reproducing the band gap energy of the compound under study.…”