Optical ultrafast characterization of copper oxide (CuO) nanocrystal charge-carrier dynamics

A thorough investigation of copper oxide, specifically cupric oxide (CuO), is performed in the following work with a focus on CuO's ultrafast free-carrier dynamics and bandstructure. An above-bandgap control beam and below-bandgap signal beam are utilized in transient absorption spectroscopy to gain insight on CuO nanocrystals' recombination and relaxation dynamics at varying control beam fluences. The authors witnessed three distinct time constants, the first of which changed with control beam fluence between 330 and 630 fs, while the second and third remained constant at 2 ps and 50 ps, respectively. The first time constant is attributed to momentum relaxation from valence band carrier-carrier scattering and exciton-exciton annihilation. The second time constant is attributed to energy relaxation from valence band carrier-phonon scattering. The third time constant is attributed to trapping and recombination as a result of the CuO nanocrystals' increased trap state density. The findings of this work provide a basis for future research on this emerging CuO nanocrystal system.