Hexagonal Boron Arsenide as a Highly Sensitive SO₂ Gas Sensor: A First‑Principles Study

Introduction

Boron arsenide (BAs) is a III–V semiconductor that combines outstanding photo‑electrical performance, robust mechanical properties, and a sizable band gap. Recent work on 2D III–V materials—including BN, AlN, GaN, GaAs, and BP—has highlighted their potential for detecting biomolecules, pollutants, and gases. 1–17 For example, AlN(0001) has been identified as a powerful catalyst for ammonia synthesis, and GaAs nanowires show strong CO₂ and N₂ adsorption. 27–29

Despite experimental synthesis and theoretical progress, the gas‑sensing capabilities of BAs remain largely unexplored. In this study, we use first‑principles DFT calculations to systematically assess the adsorption of common atmospheric gases on BAs and identify its suitability as a gas sensor, with a focus on SO₂.

Theory and Method of Simulations

The model consists of a 4 × 4 BAs supercell with a single gas molecule adsorbed. Calculations were carried out in DMol³ using the GGA‑PBE exchange‑correlation functional. A 5 × 5 × 1 Monkhorst–Pack k‑point grid and Methfessel–Paxton smearing (0.01 Ry) were employed. Atomic positions were relaxed until the total energy converged to 1 × 10⁻⁵ eV and forces were below 0.06 eV/Å. 31–33

The adsorption energy is defined as:

Ead = EBAs+gas − (EBAs + Egas)

Charge transfer was evaluated by Mulliken population analysis.

Result and Discussion

We considered three adsorption sites: atop a boron atom (B), atop an arsenic atom (As), and the center of the hexagonal ring (center). Figure 1a shows the geometry.

a Schematic of adsorption sites on BAs. b Density of states of pristine BAs.

After geometry optimization, the B–As bond length was 1.967 Å and the indirect band gap was 1.381 eV, consistent with previous reports. 34–35

Most stable adsorption configurations for each gas on BAs.

The adsorption energies, charge transfers, and equilibrium distances for all gases are summarized in Table 1.

Key observations:

• SO₂ shows the strongest adsorption (−0.92 eV) and the shortest binding distance (2.46 Å).
• NO₂ has the largest charge transfer (≈−0.09 e) and a pronounced effect on the electronic structure, turning the semiconductor into a metallic state.
• O₂ and CO₂ exhibit moderate adsorption, while N₂ and CO interact weakly.

Density of states for each gas‑BAs complex (a–i).

Electron density maps for the nine gas–BAs systems (a–i).

Work function of BAs with each adsorbed gas.

Work‑function analysis further corroborates the strong interaction of SO₂ with BAs: the pristine work function is 4.84 eV; adsorption of NO and NH₃ reduces it, while O₂, NO₂, and SO₂ increase it. These variations align with the observed charge transfer trends.

Conclusion

Our DFT study demonstrates that hexagonal boron arsenide exhibits exceptional sensitivity to SO₂ adsorption, characterized by the most negative adsorption energy, the shortest equilibrium distance, and significant charge transfer. In contrast, other gases show weaker interactions. These properties—combined with measurable changes in electronic conductivity and work function—highlight BAs as a promising, selective platform for SO₂ gas sensing.

Abbreviations

BAs

Hexagonal boron arsenide

DOS

Density of states

WF

Work function