Light-emitting metasurfaces based on direct bandgap semiconductors

Metamaterials and metasurfaces have been game-changers in the field of optics and photonics due to their various unique advantages, including their flat and compact form factor, tunable emission properties, and a rich variation of light-manipulating functionalities. Light-emitting metasurfaces based on direct bandgap semiconductors are particularly promising, as this class of devices omits the need for separate fabrication of active medium and metasurface components, allowing for more compact and efficient device architecture. In the first part of this chapter, we provide a comprehensive review of the existing and emerging fabrication processes for light-emitting metasurfaces based on direct bandgap semiconductors, highlighting the advantages and drawbacks of different processes. Following that, we summarise the different functionalities that have been demonstrated so far in these devices, which are discussed in three broad categories, namely emission enhancement, polarisation control, and directionality control. For emission-enhancing metasurfaces, we will discuss different mechanisms employed to enhance the spontaneous emission rate, create lasing cavities, and enhance the single photon emissions in direct bandgap semiconductors. Next, we will review various metasurface devices designed for the manipulation of emission polarisation, for both linear and circular polarisations. The final part of the chapter discusses various schemes to engineer the emission directionality in metasurface devices, including phased-array metasurfaces and bound state in the continuum metasurfaces with controllable emission directionality.