Abstract: Gallium sulphide (GaS) is an emerging monochalcogenide material that has recently attracted interest in optical technologies due to its tunable bandgap in the near-UV region. In this work, we employ in situ, in-operando X-ray diffraction to investigate local atomic modifications in GaS induced by 400-nm femtosecond laser pulses. We identify the energy threshold at which irreversible structural changes occur and observe a laser-induced elongation of the unit cell along the c-axis. This elongation is expected to enhance the anisotropy of the material?s physical properties. Ab initio calculations further reveal that the experimentally observed ? 10% elongation along the c-axis leads to a transition from a direct to an indirect bandgap, accompanied by a bandgap increase of approximately 0.45 eV. Additional ab-initio optical simulations show that this structural transformation results in a nearly constant in-plane refractive index contrast of Dn ? 0.1 across a wide spectral range, from the visible to the near-infrared, with negligible optical losses, which could be of interest for reconfigurable photonics applications.

Authorship

Download reference