Excited carrier relaxation in GaAs by mid-IR pump-probe spectroscopy

Ultrafast laser spectroscopy is a versatile technique that is commonly used to both understand and manipulate carrier scattering mechanisms in semiconductors. We report the observation of excited carrier relaxation times in GaAs using optical pump mid IR probe spectroscopy. We find a sharp change in relaxation times occurs at the intervalley transitions of GaAs. Our results also show the relaxation times becomes faster with increasing photoexcitation fluence. These results provide direct evidence that excited carrier decay at greatly different rates based on their energy relative to the conduction band minimum. These findings provide additional insight into the energy-dependent nature and rate of phonon emission during electronic relaxation.