The role of the buildup oscillations on the speed of resonant tunneling diodes

The fastest tunneling response in double barrier resonant structures is investigated by considering explicit analytic solutions of the time dependent Schr\"{o}dinger equation. For cutoff initial plane waves, we find that the earliest tunneling events consist on the emission of a series of propagating pulses of the probability density governed by the buildup oscillations in the quantum well. We show that the fastest tunneling response comes from the contribution of incident carriers at energies different from resonance, and that its relevant time scale is given by $\tau_r=\pi \hbar /| E-\epsilon | $, where $\epsilon $ is the resonance energy and $E$ is the incidence energy.