Ultrafast dynamics of electronic structure in InN thin film
Simultaneous measurements of transient transmission and reflectivity were performed in the unintentionally doped InN film to reveal ultrafast optical bleaching and its recovery behavior under intense laser irradiation. The optical bleaching is attributed to Pauli blocking due to the occupation of photoexcited electrons at the probing energy level. The time constant for the transition from the excitation state to the conduction band edge is $\sim$260 fs. The interplay between band filling and band gap renormalization caused by electron-hole and electron-electron interactions gives rise to complex spectral characteristics of transient reflectivity, from which the time constants of photoexcited electron-hole direct recombination and band edge recombination are extracted as $\sim$60 fs and 250$\sim$400 fs, respectively. Our results also reveal that the electron-electron interaction suppresses band edge recombination, and mitigates the recovery process. Our experiments highlight the controllability of the band structure of semiconductors by intense laser irradiation.