Simultaneous observation of “Self Trapped Exciton” and Q-confined exciton luminescence emission in silicon nanocrystals

Improvements in photoluminescence (PL) properties of silicon nanocrystals (nc-Si) obtained by Low Pressure Chemical Vapor Deposition (LPCVD) technique have been studied. In this work, 200 nm thick SiOx layers were deposited and annealed under different conditions to analyze the modifications of their luminescent properties and Fourier transform infrared (FTIR) measurements were used to complement the PL studies. The PL spectra of these samples show two main PL bands clearly related to nc-Si and their energy position shows a clear dependence on annealing conditions (atmosphere and duration), sample temperature and excitation power. Following the position of each PL band we have calculated the average nanocrystal's size by using different Q-confinement models proposed in the literature and these results were confronted to average nanocrystal's size obtained by transmission electron microscopy (TEM) measurements. Finally, these results are in good agreement with a competitive radiative recombination process between “free” excitons confined inside nc-Si and “self trapped” excitons (STE) located at the nc-Si/SiO2 interface, a simultaneous phenomenon that has not been reported yet.