Properties of silicon nanocrystals with boron and phosphorus doping fabricated via silicon rich oxide and silicon dioxide bilayers

Effects of boron and phosphorus doping on the structural, electrical, and optical properties of silicon nanocrystals in superlattice thin films were investigated. Silicon nanocrystals were fabricated via magnetron sputtering of stoichiometric silicon rich oxide and silicon dioxide bilayers followed by high temperature annealing at 1100 degrees Celsius. The characterization techniques used include: high-resolution transmission electron microscopy with energy filtering, grazing incidence x-ray diffraction, Raman, photoluminescence, and photothermal deflection spectroscopy, as well as electrical measurements. Results showed that phosphorus doping causes the loss of the bilayer structure and an increase in the average size of the silicon nanocrystals due to softening of the silicon dioxide matrix during post-sputter annealing. The result was a decrease in quantum confinement and a redshift in photoluminescence spectrum with an absorption profile similar to crystalline silicon. The undoped (intrinsic) sample maintained its bilayer structure and displayed stronger quantum confinement with higher photoluminescence peak energy and higher absorption coefficient. In-between, the boron doped sample was more similar structurally to the intrinsic sample, although merging between bilayers resulted in an extensive silicon nanocrystalline network. Optically, it displayed different effects due to photoluminescence quenching and free carrier absorption. Finally, both doped samples exhibited a decrease in electrical resistivity.