Preparation and characterization of phosphorus-doped silicon nanocrystals in SiCx films

Phosphorus (P)-doped silicon nanocrystals (Si-NCs) embedded in SiC matrix were prepared using magnetron sputtering and rapid thermal annealing with heavily P-doped Czochralski silicon as the doping target. The microstructure and electrical properties of the Si-NC thin films were characterized using transmission electron microscope, Raman spectroscopy and Hall measurement. It was observed that the microstructure changed from geometrically isolated Si-NCs to network Si-NCs with the annealing temperatures from 800 to 1200 °C. The evolution of microstructure led to the significant change of conductivity (10−6 - 101 S cm−1) in the Si0.85C0.15 thin films that possessing a fixed phosphorus concentration. A percolation threshold of crystalline-silicon (c-Si) content (30–40%) was found for the considerable increase of conductivity, where the carrier concentration dominated it. It suggested that the network Si-NCs not only increased the carrier mobility, but also boosted the carrier concentration. In addition, for the Si0.85C0.15 thin film with c-Si content above percolation threshold, the activate energy of conductivity could be lower than 70 meV and the work function lower than 4.10 eV.