BaAs₂: an arsenide with giant second harmonic generation enabled by interesting As-As bonds

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Nonlinear optical (NLO) materials are crucial for photonics and optoelectronics.
• Barium diarsenide (BaAs₂) possesses unique As-As bonds, suggesting potential for NLO applications.
• Characterization of novel semiconductor materials with NLO properties is an active research area.

Purpose of the Study:

• To report the second harmonic generation (SHG) response of BaAs₂ for the first time.
• To investigate the crystallographic and electronic structure of BaAs₂.
• To explore the origin of its NLO properties through theoretical calculations.

Main Methods:

• Single-crystal X-ray diffraction to determine crystal structure (monoclinic, Pc space group).
• Optical spectroscopy to measure the band gap (0.77 eV).
• Second harmonic generation (SHG) measurements and comparison with a known NLO material (CdGeAs₂).
• Density Functional Theory (DFT) calculations to analyze NLO contributions.

Main Results:

• BaAs₂ crystallizes in a non-centrosymmetric (NCS) monoclinic structure.
• It is a direct band gap semiconductor with a band gap of 0.77 eV.
• SHG intensity of BaAs₂ is 1.2 times that of CdGeAs₂.
• Theoretical calculations attribute the NLO effect to [As⁻] chains, with a maximum second-order NLO coefficient of 146.02 pm V⁻¹.

Conclusions:

• BaAs₂ is a novel semiconductor material with significant nonlinear optical properties.
• The As-As bonds and [As⁻] chains are key to its NLO response.
• BaAs₂ shows potential for applications in nonlinear optics and photonics.