Deep-ultraviolet Layered Oxide B2S2O9 with Strong and Robust Second Harmonic Generation

TL;DR

This paper predicts that the layered oxide B2S2O9 exhibits strong second harmonic generation and a deep-ultraviolet bandgap, with properties tunable by layer thickness and strain, opening new avenues for 2D nonlinear optical applications.

Contribution

It introduces B2S2O9 as a novel 2D material with DUV bandgap and robust SHG effects, a significant advancement over existing materials.

Findings

BSO exhibits strong SHG comparable to known DUV NLO bulks.

SHG intensity in BSO is linearly tunable by layer thickness.

Strain-induced rotations lead to nearly zero Poisson's ratios, enhancing SHG robustness.

Abstract

Two-dimensional (2D) layered semiconductors with both ultrawide bandgap and strong second harmonic generation (SHG) are essential for expanding the nonlinear optical (NLO) applications to deep-ultraviolet (DUV) region in nanoscale. Unfortunately, these materials are rare in nature and have not been discovered until now. In this Letter, we predict the B2S2O9 (BSO), an existing layered oxide, can exhibit both DUV bandgap and strong SHG effects, comparable to the best known DUV NLO bulks. The strong SHG intensities in BSO, originated from the ordered arrangement of polar SO4 and BO4 tetrahedra forming planar structure, are linearly tunable by the layer thickness. Surprisingly, the spontaneous rotations of rigid tetrahedra under strains can induce the (nearly) zero Poisson's ratios in BSO, which simultaneously result in the robust SHG effects against large strains, fundamentally differing from other known 2D NLO semiconductors. The discovery of BSO may provide an unprecedented opportunity to explore DUV NLO physics and applications in 2D limit.