Shot noise in tunneling through a single quantum dot

We investigate the noise properties of a zero-dimensional InAs quantum dot (QD) embedded in a GaAs‐AlAs‐GaAs tunneling structure. We observe an approximately linear dependence of the Fano factor and the current as a function of bias voltage. Both effects can be linked to the scanning of the three-dimensional emitter density of states by the QD. At the current step the shape of the Fano factor is mainly determined by the Fermi function of the emitter electrons. The observed voltage and temperature dependence is compared to the results of a master equation approach.

Figure 1

(Color online) (a) Current-voltage characteristics of a GaAs‐AlAs‐GaAs double barrier tunneling structure with embedded InAs quantum dots at a temperature of $T=1.5\mathrm{K}$ (black line, left axis) and shot noise amplitude $S$ as derived from averaging the curves in (b) for $f=1-10\mathrm{kHz}$ (open symbols, right axis). The scale of the right axis was chosen such that the black line corresponds on this axis to the full Poissonian shot noise $S=2\mathit{eI}$ expected for a single barrier structure. Inset: Schematic profile of the band structure at positive bias where resonant tunneling through a QD is observed. (b) Typical noise spectra of the sample for different bias voltages. The data is smoothed with a 120 Hz boxcar average. The fluctuations of the signal increase with frequency due to the capacitive loading of the current amplifier.

Figure 2

(Color online) (a) $I\text{‐}V$ characteristics for the transport through the first (I) and second (II) lowest lying resonance levels. Each corresponds to a different InAs dot in between the barriers. The dashed lines are guides to the eye to show the linear behavior of the current and its extrapolation to zero (see text). (b) Measured Fano factor $\alpha =S∕2\mathit{eI}$ of the InAs QD’s. The data have been smoothed with a five-point boxcar average. Again the dashed lines are guides to the eye for the linear behavior.

Figure 3

(Color online) (a) Modeling of the current $I$ for transport through quantum dot (II). Symbols denote measured data, lines are the result of the model [Eq. (2)], extended with contributions of QD (I) and (III). The comparison of two different temperatures demonstrates the softening of the step edge due to the Fermi distribution. (b) Same for the Fano factor $\alpha$, which is modeled by Eq. (3). The data for the Fano factor have been smoothed with a five-point boxcar average.