Ultrafast transient photoinduced absorption in Ge core and Ge/GeO2 core/shell nanoparticles: effect of interface passivation

Transient photoinduced absorption in Ge core and Ge/GeO2 core/shell nanoparticles (NPs) has been studied in visible spectral range. Two distinctive relaxation processes were observed: the fast relaxation with lifetime of several picoseconds corresponds to the carriers transfer from the excitation region to the surrounding interface or defect-related states, and the slow relaxation (tens of picoseconds) is correlated with the carriers through the interface-related states toward the indirect lowest energy states. Time-resolved studies show that the passivation of GeO2 shell significantly reduces the density of interface state and suppresses the rate of carrier trapping in Ge/GeO2 core/shell structure, which provides an alternative method to modulate the optical properties in NPs.