Carrier dynamics of excited state absorption in germanium using Mid-IR probe pulses

Semiconductors play a crucial role in various industries, and the study of carrier dynamics is essential in understanding their behavior. This manuscript presents the transient dynamics of Germanium in the transmission geometry, probed with low-energy mid-IR pulses ranging from 0.154 eV to 0.774 eV. The system is pumped with 0.953 eV, an energy greater than the band gap in the near-infrared region. Results elucidate the temporal evolution of excited state absorption (ESA) of the pump-created carrier dynamics. Excitation from the defect states to various energy levels of the band curvatures is observed with varying probe energy from the above band gap to the below band gap probing energies. For each probe energy, we extracted the pump photon flux-dependent ESA variation. In all the cases, this ESA is linearly increasing with pump power. However, the rate of increase of optical density with pump power (d(ESA)/dP) varies. This new parameter, d(ESA)/dP, is monitored for different probe energies and pump-probe delay. Interestingly, this parameter is maximum at the band gap. We believe these new experiments pave the way to understanding the intricate band structure of the excited systems.