Clustered defects in hot wire chemical vapor deposited poly-silicon films

The electron spin resonance (ESR) spectra of device quality poly-Si films (Nd=7.8×1016/cm3) made by hot wire chemical vapor deposition show only an inhomogeneously broadened single line at g=2.0055±0.0003 and peak to peak line width (ΔHpp) of 0.76 mT. This line from the sample with the smaller concentration of defects is due to isolated defects with a g-tensor anisotropy with diagonal elements gxx=2.0040±0.0003,gyy=2.0040±0.0003,gzz=2.0090±0.0003. However, for films with a larger defect density, the line width is less. A computer simulation of this ESR line shows that there are two contributions i.e., (1) a line with larger width as found for the smaller defect density materials and (2) a Lorentzian line with g=2.005±0.0003 and ΔHpp=0.5±0.01 mT. We suggest that there are two types of spin systems in the material. The temperature dependence of the magnetic susceptibility, χ, shows that there are two contributions; (i) isolated defects (dangling bonds) which follow a simple Curie function and (ii) paired spins with anti-ferromagnetic coupling with a Weiss temperature of −136.4 K. The exchange coupling energy, J, in the interaction energy between the two spins in the dimer (E=−J S1·S2), is estimated to be 9.91 meV. We propose that there are regions at the grain boundary where the defects are clustered and are close enough to allow exchange interaction. The poly-Si:H films thus appear to have such a compact structure that the defects that have to be accommodated in the region between columns have a tendency to form clusters.