Theoretical study of the electronic structure ofSiOx

A theoretical study of the electronic structure of amorphous $\mathrm{Si}{\mathrm{O}}_x$ is performed. The calculation is done using a realistic tight-binding Hamiltonian for a cluster-Bethe-lattice model. Results of the calculations are in good agreement with optical-absorption measurements for the entire range of concentrations and with photoemission spectra for $x=0,1, \mathrm{and} 2$. The nonlinear variation of the optical gap with concentration that takes place at $x=1.5\mathrm{}$ is related to the break of Si chains and to the percolation threshold. Comparison with photoemission data shows that the Si-O-Si bond angle is ∼ 125° in agreement with chemical shift analysis. Our study indicates that the distribution is Si and O atoms in $a-\mathrm{S}\mathrm{i}{\mathrm{O}}_x$ is random with no O-O bonds. It is found that intermediate range order plays a fundamental role in the electronic structure of $a-\mathrm{S}\mathrm{i}{\mathrm{O}}_x$.