Three paramagnetic defects were revealed in amorphous hydrogenated carbon-rich silicon-carbon alloy films $\left(a{\text{-Si}}_{0.3}{\text{C}}_{0.7}:\text{H}\right)$. Two of them were attributed to silicon (Si) dangling bonds (Si DBs) and carbon-related defects (CRDs). The third defect, based on its $g$-value and linewidth, was tentatively attributed to a bulk Si DB defect bonded with nitrogen atoms in ${\text{Si-N}}_2\text{Si}$ configuration. The effect of thermal vacuum annealing on the properties of the $a{\text{-Si}}_{0.3}{\text{C}}_{0.7}:\text{H}$ films was studied in the temperature range of $T_{\text{ann}}=400–950°\text{C}$. A strong increase in CRD concentration was observed in high temperature annealed $a{\text{-Si}}_{0.3}{\text{C}}_{0.7}:\text{H}$ films, which was explained by hydrogen effusion process occurred at $T_{\text{ann}}$ above $400°\text{C}$. The increase in the concentration of the CRDs is accompanied by the exchange narrowing of its electron paramagnetic resonance (EPR) linewidth due to the formation of carbon clusters having ferromagnetic ordering. The temperature dependent $g$-factor anisotropies observed at $Q$-band and $D$-band frequencies for the CRD signal in the samples annealed at high temperature $\left(950°\text{C}\right)$ were explained by the presence of graphitelike ${sp}^2$-coordinated carbon clusters and demagnetization field (shape-dependent anisotropy term). The demagnetizing field $B_{\text{dem}}=-4\pi {\text{M}}_s$, where ${\text{M}}_s$ is the sample magnetization, was found to be equal to 0.44 mT at 37 GHz and 1.1 mT at 140 GHz. Analysis of the temperature dependences of the integral intensities of the SiDB and CRD EPR signals has shown that they do not obey the Curie-Weiss law, and their spin systems exhibit superparamagnetic and ferromagnetic properties, respectively.

• Received 22 June 2009

DOI:https://doi.org/10.1103/PhysRevB.81.155319