Synthesis and characterization of boron-doped Si quantum dots for all-Si quantum dot tandem solar cells

Multiple layers of Si quantum dots (QDs) in SiO2 with a narrow size distribution were synthesized by a co-sputtering technique. Structural, electrical and optical properties of Si QD/SiO2 multilayer films with various boron (B) concentrations introduced during the sputtering process were studied. X-ray photoelectron spectroscopy (XPS) revealed B–B/B–Si bonding, which suggests possible boron inclusion in the nanocrystals. The addition of boron was observed to suppress Si crystallization, though the boron concentration was found to have little effect on the QD size. Reductions in film resistivity were observed with the increase in boron concentration, which is believed to be a consequence of an increase in carrier concentration. This is supported by a large decrease in the activation energy accompanying the drop in resistivity, consistent with the Fermi energy moving towards the valence bands. The photoluminescence (PL) intensity was found to decrease with increase in boron concentration.