Improved vertically integrated resonant tunneling diodes

A lumped-element circuit model is developed for vertically integrated resonant tunneling diodes (RTDs), assuming that the individual RTDs behave as independent circuit elements in vertically integrated RTDs. The limit of this model is determined and the transition between incoherent and coherent transport is observed by systematic variation of separation layer thickness between diodes. The limit of applicability of this model is determined to be devices with 500 AA separation for 10/sup 18/ cm/sup -3/ doping. High current density is identified as a critical parameter for high-speed operation, and a peak current density of 2.5*10/sup 4/ A/cm/sup 2/ was achieved with little degradation in the peak to valley ratio by using thin barriers. Approaches for further improvement are suggested.<>