Impact of Small-Angle Scattering on Ballistic Transport in Quantum Dots

Disorder increasingly affects performance as electronic devices are reduced in size. The ionized dopants used to populate a device with electrons are particularly problematic, leading to unpredictable changes in the behavior of devices such as quantum dots each time they are cooled for use. We show that a quantum dot can be used as a highly sensitive probe of changes in disorder potential and that, by removing the ionized dopants and populating the dot electrostatically, its electronic properties become reproducible with high fidelity after thermal cycling to room temperature. Our work demonstrates that the disorder potential has a significant, perhaps even dominant, influence on the electron dynamics, with important implications for “ballistic” transport in quantum dots.

Figure 1

(a)–(b) Scanning electron micrographs of undoped device $U1$ and modulation-doped device $M1$ with 500 nm scale bars (white). Green and red tinted regions in (a) indicate the $n^{+}$ GaAs top and side gates. Yellow tinted regions in (b) are Ti/Au gates on the heterostructure surface.

Figure 2

Magnetoconductance $G(B)$ vs perpendicular magnetic field $B$ for $M1$ with $V_{\mathrm{SG}}=-443.5\mathrm{mV}$ before (blue) and after (red) thermal cycling to $T=300\mathrm{K}$. The red trace is vertically offset by $-0.6$ for clarity.

Figure 3

$G(B)$ vs $B$ for $U1$, increasing $V_{\mathrm{TG}}$ from $+930$ (top) to $+955\mathrm{mV}$ (bottom) in 5 mV steps, (a) before (black) and (b) after (red) thermal cycling to $T=300\mathrm{K}$. Traces in each panel are sequentially offset by $+0.5$ vertically from the bottom (0) to top ($+2.5$) for clarity.

Figure 4

(a) Extracted magnetoconductance fluctuations $\delta G$ vs $B$ for $U1$ (uppermost left trace in Fig. 3—thick black line) and $M1$ (uppermost trace in Fig. 2—thin blue line). The $U1$ data are vertically offset by $+0.4$ for clarity. (b) Fourier power spectra and (inset) normalized autocorrelation functions obtained for the two traces in (a).