Carrier relaxation is a research area focused on understanding the dynamics of charge carriers (such as electrons or holes) in a material after they have been excited by an external stimulus, such as light or electrical currents. The study of carrier relaxation involves investigating how carriers lose their excess energy through processes such as phonon emission, impact ionization, or recombination. This area of research is important for a wide range of applications, including semiconductor devices, solar cells, and photo-detectors, as it can help optimize the efficiency of these devices by understanding and controlling the relaxation mechanisms of carriers.