CaSTL Seminar with Richard D. Schaller

Excess carrier energy, which many aim to utilize for advanced energy conversion technologies, rapidly dissipates from electrons and holes in both bulk and quantum confined semiconductors despite expectation of slowed cooling in the latter.  We attempt to characterize rates and modes of dissipation available to carriers via time-resolved optical spectroscopies including femtosecond stimulated Raman spectroscopy (FSRS) and time-resolved photoluminescence. Using FSRS, we characterize longitudinal optical (LO) phonon production and dissipation throughout the process of confinement-enhanced, ultrafast intraband carrier relaxation. Upon excitation, we observe a decrease in stimulated Raman amplitude and note a size-independent LO phonon formation time. Mode softening is observed along with evidence of phonon down-conversion processes. Furthermore, spectrally and temporally resolved photoluminescence suggest evidence of acoustic phonon dissipation times that follow diffusive transport, which we can manipulate. This new means of thermalization manipulation offers route to advance thermoelectric and LED devices.