Multiexcitons

Multiexcitons are excited states in a material that involve more than one electron-hole pair. In typical semiconductors, absorption of a photon with sufficient energy creates a single electron-hole pair, known as an exciton. However, in certain materials or under specific conditions, the absorption of a single high-energy photon can generate multiple excitons. This phenomenon is known as multiexciton generation (MEG).

MEG is a nonlinear optical process. The efficiency of MEG depends on factors such as the material's electronic band structure, the energy of the incident photon relative to the band gap, and the material's morphology. Quantum dots, which are semiconductor nanocrystals, are particularly well-known for exhibiting strong MEG. The quantum confinement in these small structures can significantly alter their electronic properties, favoring the creation of multiple excitons.

The study of multiexcitons is important for various technological applications. For instance, MEG can enhance the efficiency of solar cells by allowing a single high-energy photon to generate more than one electron-hole pair, thereby potentially exceeding the Shockley-Queisser limit for single-junction devices. It also plays a role in photodetectors and light-emitting diodes, where understanding and controlling the generation and recombination of multiexcitons can lead to improved performance. Research into multiexcitons continues to explore new materials and methods to harness this phenomenon for advanced optoelectronic devices.