Resonant tunneling through the bound states of a single donor atom in a quantum well

A series of sharp peaks is observed in the low-temperature I(V) characteristics of a gated 1 x 1-micron GaAs/(AlGa)As resonant tunneling diode, in which the gate is used to reduce the effective cross-sectional area from 0.7 to less than 0.1 sq micron. These peaks, which occur at voltages well below the calculated resonant threshold, show a weak dependence on temperature, magnetic field, and cross-sectional area. This subthreshold structure is argued to be due to an inhomogeneity which gives rise to a localized preferential current path, and the spatial extent of the inhomogeneity is approximately 25 nm. The likely origin of the inhomogeneity is a donor impurity in the quantum well. (Author)