We report magnetotunneling through a quantum dot realized in a 200-nm-diameter ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs double-barrier diode. Steplike current-voltage characteristics are observed at low temperatures in the low-bias regime and are assigned to tunneling though zero-dimensional states. With increasing magnetic field parallel to the current direction, the first six resonances shift to higher bias by the same amount. The data are discussed in terms of a simple model of electrostatic quantum confinement in a magnetic field, allowing for Coulomb-charging effects. We conclude that a more detailed theory is needed to obtain a clear explanation of the mechanism leading to the current steps.

• Received 9 March 1992

DOI:https://doi.org/10.1103/PhysRevB.46.3948