Tunneling Current Structure Resolution by Differentiation

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Abstract
Structure in the current‐voltage characteristics of heavily doped p‐n junctions and superconductor junctions is more clearly revealed if the current is differentiated with respect to the voltage and is still more clearly revealed if a second differentiation is performed to obtain d2I/dV2. This paper describes a working system for automatically measuring and continuously plotting these derivatives as a function of voltage. Traces of current‐voltage characteristics of heavily doped degenerate p‐n junctions and the first and second derivatives of these characteristics obtained by the techniques described are given. A series of first derivative curves for an Al‐Al2O3‐Pb tunnel junction is also included to illustrate the speed of the method.