Inductive to capacitive ac behavior of nanocrystalline silicon wires

Abstract

The ac response of nanometer sized silicon percolating pathways, embedded into a silicon oxide matrix, was studied. CW laser treatments, performed on substoichiometric hydrogenated amorphous silicon oxide films, were used to induce silicon nanocrystals formation by solid state crystallization. A contact structure, probing the material along the laser treated traces, was employed. The real part of admittance showed a resonance-like response. The initial observation of a resistive behavior is followed by a decrease, reminiscent of an inductive effect, eventually turning into a further increase, typical of a capacitive behavior. The imaginary part of impedance and electric modulus showed temperature dependent Lorentzian peaks, 1.14 decades wide at half-maximum, with the same most probable hopping frequency and average barrier height equal to 0.22 ± 0.02 eV. On the other hand, loss tangent spectra addressed resistive losses, only. The conductivity relaxation time was found to be Arrhenius activated, with τ 0 = 8.2 ns, as the most probable hopping frequency. Analysis of such results supported the idea of an “apparent” inductivity related to a frequency dependent polarization state of defects located at the grain boundaries, which are mainly constituted by a residual thin layer of silicon oxide.