Observation of resonant tunneling through a compositionally graded parabolic quantum well

Abstract

We report the first observation of electron resonant tunneling through parabolic quantum wells, compositionally graded by means of short‐period (15 Å) Al_xGa_1−xAs/GaAs superlattices grown by molecular beam epitaxy. In one structure, comprising a 300‐Å‐wide well compositionally graded from AlAs to GaAs, five equally spaced resonances are observed in the current‐voltage (I‐V) characteristic in good agreement with the theory. In another structure with 432‐Å‐wide wells graded from Al_0.30Ga_0.70As to GaAs, up to 16 resonances are observed in the I‐V. The first ten correspond to resonant tunneling through the quasi‐bound states of the double barrier while the others are ascribed to electron interference effects associated with virtual levels in the quasi‐continuum energy range above the collector barrier.