Explanation of the structural changes in the Si: H thin films by monohydride cluster formation

We have studied the structural changes in Si: H thin films under conditions of increasing SiH4 depletion for three different sets of SiH4-Ar mixtures in the ratios 10: 90, 5 : 95, 1 : 99, respectively by varying the power density in plasma enhanced chemical vapour deposition. The structural properties of the deposited Si: H materials have been studied by Fourier transform infrared spectroscopy, small angle x-ray scattering and transmission electron microscopy. It was observed that the shift in the SiH stretching mode frequency has a one to one correspondence with the changes in the microstructures in the films. This shift has been explained on the basis of the changes in the electronegativity of the matrix due to monohydride cluster formation in the neighbourhood of a SiH bond. It has been observed that the onset of microcrystallites formation coincides with the maximum shift of the SiH stretching mode frequency. The role of Ar* in mediating the structural changes with dilution and power density have been discussed.