Relation between Electronic Properties and Density of Crystalline Agglomerates in Microcrystalline Silicon

Abstract

AbstractA series of silicon thin films was made by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at substrate temperatures below 100 °C at different hydrogen to silane dilution ratios. The electronic properties of these layers were studied as a function of the surface crystalline fraction as determined accurately from a combination of microscope images at different length scales (gathered by using different types of microscopes). The results show that the electrical conductivity increases monotonously as a function of crystalline surface coverage and no discontinuity is observed at the percolation threshold. An increase in conductivity of four orders of magnitude for layers with a high crystalline content is observed after annealing at temperatures up to 170 °C. Combined with the information that oxygen is incorporated at Si-H surface bond sites, this suggests that doping of the intergrain boundaries by oxygen might be dominantly responsible for the electronic properties of mixed phase silicon.