Current fluctuations in single barrier vertical GaAs/AlAs/GaAs tunneling devices

We report the experimental results of the low temperature (T = 4.2 K) low-frequency current fluctuations measurements in the single-barrier resonant tunneling GaAs/AlAs/GaAs device with Si delta-doping in the center of the 10 nm thick AlAs barrier. The dimensions of the device were 200 mu m by 200 mu m. For the biasing voltages 0.1 V < vertical bar U vertical bar < 1 V we observed the Fano factors between F = 0.7 and F = 0.95. We explain it by the existence of the trapping centers/imperfections/resonant levels inside the barrier participating in the transport for this range of voltages. Only for the smallest biasing voltages the Fano factor tends to F = 1, expected for a highly nontransparent barrier.