Transient absorption signatures of asymmetric carrier cooling in semiconductors.

Electron cooling dominates femtosecond transient absorption in GaN and GaAs, occurring on characteristic timescales on the order of 100 fs and governed by optical-phonon scattering.

• Why it matters: Pump-probe transient absorption typically measures combined electron–hole responses, making it difficult to resolve individual cooling dynamics needed for electronics, optoelectronics, energy, and quantum technologies.
• What they did: The authors combine high time-resolution femtosecond TA spectroscopy with quantitative first-principles simulations in wurtzite and zinc-blende semiconductors to disentangle electron versus hole cooling signatures.
• The result: Simulations predict hole cooling is one order of magnitude faster yet contributes comparatively weakly to the TA response, revealing asymmetric carrier cooling as a general feature of direct-gap wurtzite and zinc-blende semiconductors.