Observation of negative differential resistance due to tunneling through a single barrier into a quantum well.

We have observed a negative differential resistance (NDR) in a single-barrier tunneling structure in which electrons tunnel from a doped-semiconductor emitter layer into a quantum-well (QW) layer, and subsequently drift laterally to a specially designed contact. Pronounced NDR is seen already at room temperature, and at 77K the peak-to-valley (PTV) ratio in current is more than 2:1. Our results lend support to a recent hypothesis by Luryi that the NDR in double-barrier tunneling structures is not related to a resonant enhancement of the tunneling probability at selected electron energies, but rather originates from tunneling into a system of electronic states of reduced dimensionality. For comparison we have also fabricated a QW structure with two tunneling barriers, in which the parameters of the emitter barrier and the QW are identical to those in the single-barrier structure. In the control double-barrier structure we have obtained current densities as high as [EQ] 4 times 10 sup 4 A/cm sup 2[EN] and an NDR with PTV ratios of 3:1 at 300 K and 9:1 at 77 K.