Influence of doping and microstructure on electrical properties of doped silicon thin films

In this work, phosphorus and boron doped silicon films were deposited on monocrystalline silicon substrates by plasma enhanced chemical vapour deposition. Microstructure and net doping concentration were investigated using Raman spectroscopy and secondary ion mass spectrometer, and the dark conductivity, carrier concentration and mobility of the films were measured using semiconductor characterisation system. The results indicated that the structure of the films were all amorphous despite of the different doping gas flow ratios, and the dark conductivity and carrier density changed by only one order of magnitude with the increase in [PH₃]/[SiH₄] and [B₂H₆]/[SiH₄] gas flow ratios. The best flow ratios of [PH₃]/[SiH₄] and [B₂H₆]/[SiH₄] were obtained to be 1.5 and 1% respectively, and then the optimised samples were annealed. After annealing, the film expressed a tendency of transition to crystalline from amorphous according to the Raman results, and the dark conductivity and carrier concentration increased by two to three orders of magnitude for both doped film series. The structure has more significant influence on the electrical properties of doped silicon thin film than the doping concentration.