Small-signal Theory of Space-charge-limited Diodes†

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Abstract
A unified approach for small-signal theory of spaee-charge-limited (SCL) unipolar diodes is suggested. SCL planar vacuum diode and SCL solid-state diodes with various velocity field-dependences are taken into account. The typical small-signal method used allows us to solve problems, both already studied and new, of SCL diodes' small-signal operation in a simple and direct manner. As an illustration of this method, the SCL solid-state diode having a carrier velocity field-dependence of the form υ = μEc(E/Ec)m (0≤M≤1) is studied in detail. The impedance of SCL dielectric diodes with traps, taking into account both trapping and transit-time effects, is presented. A method of physical interpretation of small-signal SCL diodes' response is suggested and the possibility for the appearance of a high-frequency negative conductance is discussed. Particularly, the negative conductance calculated for the dielectric diode with a high density of shallow traps is explained.