Microstructure and Hydrogen Dynamics in a-Si_1-xC_x:H

Abstract

Small angle x-ray scattering (SAXS), IR spectroscopy, and deuterium secondary ion mass spectrometry (DSIMS) were used to study the microstructure and hydrogen dynamics of undoped and boron-doped if-sputter-deposited (RFS) and electron cyclotron resonance (ECR)-deposited hydrogenated amorphous silicon carbides (a-Si_1-xC_x:H) with x ≤ 19 at.%. The SAXS measurements indicated residual columnar-like features and roughly spherical nanovoids of total content C_nV ≤ 1.0 vol.%. The growth of C_nV with annealing was due largely to an increase in the average nanovoid radius. It was noticeably smaller than in RFS a-Si:H films. The IR spectra demonstrated H transfer by annealing from mostly bulk-like Si-H groups to C-bonds. The H diffusion and its temperature dependence in undoped films resembled those of a-Si:H and were consistent with the SAXS and IR data. Suppression of long-range motion of most of the H atoms, consistent with increased C_nV was observed in B-doped ECR films. However, a small fraction of the H atoms appeared to undergo fast diffusion, reminiscent of the fast diffusion in doped a-Si:H. The results are consistent with impeded relaxation processes of the Si network, caused by the presence of C atoms, and H trapping at C-H bonds.