Formation and photoluminescence of Si quantum dots in SiO2/Si3N4 hybrid matrix for all-Si tandem solar cells

In this work, Si quantum dots in SiO2/Si3N4 hybrid matrix on quartz substrates were synthesized by magnetron sputtering of alternating silicon rich oxide and Si3N4 layers followed by different post-deposition anneals. XRD results indicate that the average dimension of the Si nanocrystals varies from 1.6 to 5.2 nm. The size and crystallization of the Si nanocrystals are dependent on a number of factors, including the annealing method, the SRO thickness and the Si3N4 barrier thickness, as evidenced in XRD and Raman measurements. In particular, thicker Si3N4 barrier layers seem to be able to suppress the growth of Si nanocrystals more effectively. PL measurements suggest the apparent bandgap of the samples investigated in this work is in the range 1.12–1.67 eV, which demonstrates the effect of quantum confinement. More interestingly, analysis of the PL data using the modified EMA equations clearly suggests that the PL peak energy not only depends on the size of the nanocrystals but also gets affected by other details in nanocrystal growth. A tentative core–shell model is constructed to illustrate our explanation. These findings offer a preliminary understanding of the nanocrystal growth and radiative recombination processes in this newly synthesized material for photovoltaic applications.