Field ionization of deep levels in semiconductors with applications to Hg1−xCdxTe p-n junctions

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Abstract
Deep level‐to‐band tunneling is investigated as a source of excess current in narrow band semiconductors with specific application to Hg1−xCdxTe. The theoretical modeling is carried out by analogy with the Oppenheimer approach to the field ionization of hydrogen and the resulting expression for the transmission matrix element is found to be an improved version of the one originally derived by Price and Sah. The tunneling rate characteristics are governed primarily by the exponential term which is calculated using ‘‘exact’’ E‐k dispersion relations combined with a parabolic barrier field. The preexponential term displays a marked insensitivity to both deep level energy and choice of impurity potential for near midgap states. Application of the theory to find the generation‐recombination rate for the process leads to the anticipated ‘‘bump’’ in the forward bias I‐V characteristics of pn junctions for a suitably chosen range of device parameters. The first direct experimental observation of just such a bump in Hg1−xCdxTe diodes is also reported in this paper.