Carrier capture times of the localized states in an InGaN thin film with indium-rich nanocluster structures

A femtosecond nondegenerate pump-probe technique of using two beta barium borate crystals for frequency doubling a $7fs$ Ti:sapphire laser is used for studying the ultrafast carrier dynamics in an InGaN thin film, in which nanoscale indium-rich clusters have been observed. The carrier capture time of the localized states (the cluster states) from the free-carrier states (the states of the background compound) is calibrated. The initial rise times of the differential transmission of the probe intensity are calibrated to give the time constant of about $300fs$ for the degenerate cases over the whole photoluminescence spectral range and for the nondegenerate cases, in which both pump and probe wavelengths correspond to the free-carrier states. However, when the carriers are excited in the free-carrier states and probed in the localized states, the rise time increases to the range of $590–715fs$⁠, which represents the carrier capture time of the localized states from the free-carrier states.