Comparison of picosecond electron dynamics in isolated and clustered Si quantum dots deposited on a semiconductor surface

Semiconductor quantum dots (QDs) have been widely used in various optoelectronic devices. Extensive studies have been devoted to the application of Si QDs with the aim of realizing various optoelectronic functions based on the modified energy band structure in QDs compared with bulk crystals. Therefore, it is necessary to be able to directly probe the carrier dynamics in single Si QDs of nanoscale dimensions deposited on a SiO₂/Si surface, where the environment is compatible with Si-based semiconductor devices. This letter reports the observation and comparison of the ultrafast electron dynamics just after the photoexcitation of isolated and clustered Si QDs on a SiO₂/Si surface using time-resolved photoemission electron microscopy with spatial and temporal resolutions of 50 nm and 100 fs, respectively. The detailed structure of QDs was confirmed directly by scanning electron microscopy observations. The results obtained in the present study show that the carrier lifetime in isolated QDs is shorter than that in clustered QDs. This is consistent with the electron-hole interaction in nanospace, significantly modifying the carrier recombination rates.