Native defect-related broadband ultrafast photocarrier dynamics in n-type β -Ga₂O₃

We report two-photon excited ultrafast carrier trapping and recombination in n-type β-Ga2O3 crystals by using femtosecond transient absorption spectroscopy. The broadband absorption spectra arising from the defect are polarization dependent, especially, two absorption peaks can be observed by subtracting the absorption transients under two probe polarizations. We attribute these observed defect-related absorption features to optical transitions from the valence band to different charge states of a native defect (such as gallium vacancies). A model for carrier capture by multilevel of a single defect is proposed to interpret the data, wherein holes are captured more efficiently than electrons by the defects, and the absorption cross sections for the defects are at least ten times larger than that for free carriers. Our results reveal the potential applications of β-Ga2O3 in ultrafast and broadband optoelectronic devices.