hotcarrier

Hot carrier refers to a charge carrier in a solid whose energy distribution is not in thermal equilibrium with the lattice, i.e., an electron or hole with an effective temperature higher than the surrounding material. Hot carriers arise when energy is deposited into the electronic system faster than it can equilibrate with the lattice, such as from absorption of high-energy photons, strong electric fields, or the decay of plasmon resonances in metals.

In semiconductors and nanostructures, hot carriers can persist briefly before scattering processes redistribute energy among electrons and then to phonons. Electron–electron interactions rapidly thermalize the carrier ensemble to a quasi-equilibrium at a higher temperature, followed by electron–phonon coupling that cools the electrons toward the lattice temperature. Cooling times are typically sub-picosecond to a few picoseconds in many materials, but can be longer in engineered nanostructures, two-dimensional materials, or certain heterostructures.

Applications and research areas include hot-carrier solar cells, which aim to extract photogenerated carriers before they thermalize in order to surpass conventional efficiency limits. In photodetection and photocatalysis, hot carriers from plasmonic or quantum-confined structures can drive chemical reactions or produce currents before losing excess energy. In metals, hot electrons and holes contribute to plasmonic and nonthermal photoresponse phenomena.

Measurement and study of hot carriers employ ultrafast spectroscopy, such as pump–probe techniques, and time-resolved photoemission methods to track non-equilibrium carrier distributions. Material platforms span traditional semiconductors, perovskites, graphene, and metal nanoparticles.

Key challenges include achieving practical extraction of hot carriers and suppressing rapid cooling, which currently limits device performance. As a research topic, hot carriers remain primarily in the experimental and theoretical exploration stage with few commercial implementations.