Single-electron transport in small resonant-tunneling diodes with various barrier-thickness asymmetries

We fabricated submicrometer-diameter double-barrier diodes from four wafers with different barrier-thickness asymmetry. All samples exhibit staircaselike features in the current-voltage characteristic at the current threshold due to single-electron tunneling. Our study focuses on the properties of the first current step which arises from tunneling through the energetically lowest discrete electron state within the double-barrier region. The analysis of the bias position of the step allows a spatial spectroscopy of the vertical position of the lowest discrete level in the double-barrier region. The magnitude of the step is in excellent agreement with theory for all barrier-thickness asymmetries whereas the broadening of the step edge exceeds the lifetime-related width of the discrete state by one order of magnitude.