Photoluminescence Enhancement of InSe by Coupling with Circular Bragg Grating

Indium selenide (InSe) has attracted tremendous research interest due to its excellent optical and electronic properties. The direct bandgap of bulk InSe promises efficient carrier recombination in the near-infrared (NIR) spectral range, holding great potential for NIR-based optoelectronic device applications. However, the lowest energy transition in InSe involves out-of-plane optical dipoles, with resulting photoluminescence (PL) transmitted mainly along the layer plane. This limits both optical excitation and detection efficiency along the surface normal for practical device operation. To circumvent this issue, here, bulk InSe flake is coupled with circular Bragg grating (CBG) fabricated on silicon substrate by focused ion beam milling. A maximal 60-fold PL enhancement is achieved, with Purcell effect-facilitated carrier recombination and improved light out-coupling via CBG contributing jointly. The same device architecture is further demonstrated to boost the second harmonic generation by a factor of 34. The results provide an effective way to enhance the optical performance of III-VI layered nanomaterials for both linear and nonlinear optoelectronic device applications.