Exciton formation dynamics at the SiO2/Si interface

Abstract

Excitons can operate as carriers for energy transduction in optoelectronics, and engineering their dynamics is of great interest. Here, we employ time-resolved terahertz spectroscopy to analyze exciton formation dynamics as a function of temperature for a (100) N-type silicon substrate passivated by native SiO2. By analyzing the frequency-resolved complex conductivity as a function of temperature we resolve the photophysics for the formation of free carriers into excitons. Notably, we observe a relatively long-lived ~300 ps transient population of free carriers at temperatures well below the Mott transition (4 K). We rationalize this by transient photophysics at the SiO2/N-type-Si surface, where holes localize and release under high injection conditions due to a transient surface photovoltage effect. We believe our results have implications for the design of excitonic-based electronic applications operating at cryogenic temperatures and accessed optically.