Depletion layer amplification from negative differential mobility elements

Recent n-GaAs experiments and computer simulations have demonstrated that amplification from "supercritical" negative differential mobility (NDM) semiconductors is dependent on the shape of the dc stable electric field versus distance profile. For a specific nonuniform field profile, where a partially depleted charge layer is adjacent to the cathode, we show that small-signal amplification from 10-µ-long 10¹⁵/cm³NDM elements is 1) dependent upon conditions at the cathode boundary, 2) dc bias dependent, 3) arises from a subcritical region of the element, and 4) has a frequency band for small-signal negative resistance that is determined by the transit time of the carriers across the depleted region.