Nature of the Valley Current in Tunnel Diodes

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Abstract
An explanation of the ``excess current'' up to and including the valley point, observed in tunnel diodes, is suggested in terms of tunneling between impurity band states of the heavily dopedp and n regions. Density‐of‐states curves are constructed, based on several different models of impurity bands, and the tunneling current between such bands is computed and compared with experiment. The effect of different base materials and impurities on the valley current is discussed. Some aspects of impurity band formation in heavily dopedsemiconductors are considered, and possible modifications and difficulties of the present approach are indicated. The possibility of obtaining information about impurity band structure from tunnel diodemeasurements is discussed. Experimental evidence is presented about the position of the Fermi level in heavily dopedsemiconductors and is shown to agree with that postulated by the present model. The Appendix gives the theory of locating the Fermi levels from measurements of the temperature variation of the diode characteristic.