24 May 1999 Ultrafast carrier dynamics in GaN epilayers studied by femtosecond pump-probe spectroscopy
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Femtosecond pump-probe measurements were performed in GaN epilayers to study carrier dynamics in the band edge region. Excitonic absorption was found to begin saturating at a pump fluence of 20 (mu) J/cm2 which corresponds to an estimated carrier density of 1 X 1018 cm-3. At zero delay between pump and probe, induced absorption is observed below the unpumped band gap due to ultrafast bandgap renormalization. After 375 fs, a large induced transparency is observed just below the excitonic resonance which is due to a transient electron-hole plasma. After 1 ps, the absorption has partially recovered to a level associated with excitonic phase-space filling. The absorption then recovers with a characteristic time of approximately 20 ps, a value which increases with increasing excitation density.
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Arthur J. Fischer, Brian D. Little, Theodore J. Schmidt, Chan-Kyung Choi, Jin-Joo Song, Robert D. Horning, Barbara L. Goldenberg, "Ultrafast carrier dynamics in GaN epilayers studied by femtosecond pump-probe spectroscopy", Proc. SPIE 3624, Ultrafast Phenomena in Semiconductors III, (24 May 1999); doi: 10.1117/12.349293; https://doi.org/10.1117/12.349293

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