Effects of field enhanced charge transfer on the luminescence properties of Si/SiO2 superlattices

Abstract

The effect of an externally applied electric field on exciton splitting and carrier transport was studied on 3.5 nm Si nanocrystals embedded in SiO2 superlattices with barrier oxide thicknesses varied between 2 and 4 nm. Through a series of photoluminescence measurements performed at both room temperature and with liquid N2 cooling, it was shown that the application of an electric field resulted in a reduction of luminescence intensity due to exciton splitting and charging of nanocrystals within the superlattices. This effect was found to be enhanced when surface defects at the Si/SiO2 interface were not passivated by H2 treatment and severely reduced for inter layer barrier oxide thicknesses above 3 nm. The findings point to the surface defects assisting in carrier transport, lowering the energy required for exciton splitting. Said enhancement was found to be diminished at low temperatures due to the freezing-in of phonons. We propose potential device design parameters for photon detection and tandem solar cell applications utilizing the quantum confinement effect based on the findings of the present study.