Electronic properties of doped silicon nanocrystal films

The structural and electrical properties before and after laser annealing of spin-coated films of doped silicon nanocrystals (ncs) produced from the gas phase are presented. While the as-deposited films form a porous network of ncs and show only weak electrical conductivity independent of the doping level, a laser annealing step leads to sintering and melting of the particles and tremendously increases the lateral conductivity. By controlled doping of the initial particles, the conductivity can be further enhanced by seven orders of magnitude reaching values of up to 5 -1 cm-1. The conductivity is found to increase with the doping concentration for highly doped samples while it is independent of the doping level below a critical concentration of 1019 cm-3. The results are discussed within a compensational model taking into account the defect concentration from electron paramagnetic resonance measurements and the activation energies of the electrical conductivity. Surface segregation of phosphorus during growth is identified as the origin of the apparently small phosphorus doping efficiency.