Quantum mechanical tunneling has a wide range of practical applications [1] .One of these is the normal metal-insulator –superconductor (MIS)[2].The normal metal and super conductor may take density of states of a two-dimensional character [3] having the usual three singularities [4], which are the minimum, the maximum and the saddle point. Both maximum and minimum are of step like form and the saddle point is of logarithmic –like form. Practically the step singularity is weakened to the square root one [5].In recent years remarkable applications in optoelectronic devices using nanostructure materials utilize the two- dimensional character of the density of states. The current voltage characteristics in MIS or other kinds of multi-layers are often desired to fine or weak the current by using modulation spectroscopy, which can be divided into three kinds which are amplitude, frequency, phase modulations [6].
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