Diode Theory in the Light of Hole Injection

Classical diode theory, as applied to metal point contacts made to an n-type semiconductor, is adequate only for small forward voltages at which, under certain conditions, hole current may be negligible. The shape of the theoretically predicted diode characteristic is not affected by the hole injection process at low voltages, no matter what the composition of the current. However, for voltages in excess of a certain value, dependent only on the resistivity of the material (on the order of 0.1 volt for 5 ohm-centimeter germanium), the spreading resistance is comparable to the barrier resistance, and it is the hole injection process which accounts for continued rectification. The extent to which the spreading resistance is decreased by hole injection depends on the ratio, γ, of hole current to total current. The present paper includes a theory of the effect of this ratio on the diode characteristic at higher forward voltages. A method of measuring γ from V-I characteristics alone is indicated.