Effect of microwave radiation on conductivity of porous silicon nanostructures

An attempt was made to find out the possible influence of microwave radiation on the conductivity of structures containing porous silicon layers. Samples have been made of boron doped p-type, (100) oriented, p = 0.4 Omega.cm specific resistance silicon wafers by technology involving electrochemical etching in HF: ethanol = 1: 2 electrolyte, and subsequent preparation of contacts. Two kinds of prepared samples have been characterized by nonlinear and linear current-voltage characteristics. Electric conductivity of the samples was investigated under the action of 10 GHz frequency microwave radiation. Activation nature of porous silicon conductivity was revealed. Model of hopping conductivity in the vicinity of Fermi level in the lattice of a porous silicon grid, considering the fractal character of porous silicon skeleton, has been applied to explain experimental results. Three activation energies were found: E-0', E-0 '' and E-0''' (E-0' < E-0 '' < E-0'''), caused by fractal character of a porous silicon grid. Activation of conductivity occurs because of charge carrier heating in porous silicon structure by microwave radiation.