Raman studies of aluminum induced microcrystallization of n⁺ Si:H films produced by PECVD

We performed a Raman scattering study of aluminum induced microcrystallization of thin films of phosphorous-doped hydrogenated amorphous silicon (n⁺ a-Si:H). These thin films of heavily doped n⁺ a-Si:H were prepared by plasma enhanced chemical vapor deposition. Afterwards, aluminum was deposited and followed by an annealing process at 523 K in a nitrogen environment during several hours. Raman results reveal the formation of microcrystalline regions distributed in the amorphous matrix, induced by the film annealing in the presence of the aluminum. We have used the spatial correlation model to estimate from the Raman signal the microcrystallite size and its relation with the annealing time. The estimated crystallite size was found to be between 6.8 and 9.5 nm and the broadening and downshift of the signals are explained in terms of the crystallite size and lattice expansion effects due to the annealing process. Conductivity values of the samples as a function of the annealing time are explained in terms of the contributions from the amorphous and from the microcrystalline phases.