Shot noise enhancement in resonant-tunneling structures in a magnetic field

We have observed that the shot noise of the tunnel current, {ital I}, in a GaSb-AlSb-InAs-AlSb-GaSb double-barrier structure under a magnetic field can exceed 2qI. The measurements were done at T=4 K in fields up to 5 T parallel to the current. The noise enhancement occurred at each of the several negative-differential conductance regions induced by the tunneling of holes through Landau levels in the InAs quantum well. The amount of the enhancement increased with the strength of the negative conductance and reached values up to 8qI. These results are explained qualitatively by fluctuations of the density of states in the well, but point out the need for a detailed theory of shot noise enhancement in resonant-tunneling devices. {copyright} {ital 1998} {ital The American Physical Society}