Capacitive-Coupling-Enhanced Switching Gain in an Electron Y-Branch Switch

We have fabricated electron Y-branch switches (YBS) on modulation doped $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures. The Y branch consists of a one-dimensional source, which is split along the branching section into two one-dimensional drains. In addition to source drain voltages, external electric fields can be applied via gates along the branches.In the nonlinear transport regime sweeps of the side-gate voltages lead to a voltage difference between the drain reservoirs with gain. This switching gain increases superlinearly with the bias voltage applied between the source and the drains of the YBS. We explain the bias voltage enhanced switching by a capacitive coupling of the branches.

Figure 1

Scanning electron microscope (SEM) image of a YBS with a length $l=70\mathrm{n}\mathrm{m}$ of the branching section and a schematic view of the measurement configuration. Separated by etched trenches from the nanojunction the left and the right side-gate allow one to direct electrons into either of the branches. The bias voltage $V_{\mathrm{b}\mathrm{i}\mathrm{a}\mathrm{s}}$ was applied via two resistors ($R_b=10\mathrm{M}\mathrm{\Omega }$) to the left and the right branch of the YBS, with the stem coupled to ground via $R_s=120\mathrm{k}\mathrm{\Omega }$. High impedance voltmeters were used to measure the voltage $V_{st}$ at the stem as well as the voltages $V_{bl}$ and $V_{br}$ at the left and the right branch, respectively. All voltages are related to ground.

Figure 2

(a) Voltages $V_{bl,r}$ detected at the left and the right branch reservoir vs the voltage difference $\Delta V_g=V_{gl}-V_{gr}+V_{g,\mathrm{a}\mathrm{s}\mathrm{y}\mathrm{m}}$ varied in push-pull fashion, i.e., $\delta V_{gl}=-\delta V_{gr}$. (b) Voltage difference $\Delta V_b=V_{bl}-V_{br}$ at the branches versus $\Delta V_g$ and the gate voltage $\Delta V_{g,\min }$ needed to switch from $\Delta V_b=0.5V_{\mathrm{b}\mathrm{i}\mathrm{a}\mathrm{s}}$ to $\Delta V_b=-0.5V_{\mathrm{b}\mathrm{i}\mathrm{a}\mathrm{s}}$ as a function of $V_{\mathrm{b}\mathrm{i}\mathrm{a}\mathrm{s}}$ (inset). The calculated curve corresponds to ${\eta }_g/V_s=10.0{\mathrm{V}}^{-1}$, ${\eta }_b/V_s=-0.36{\mathrm{V}}^{-1}$, $G=1.16\times {10}^{-6}{\Omega }^{-1}$, and $V_{wp}=0.10\mathrm{V}$.

Figure 3

Differential voltage gain $g$ as a function of the gate voltage difference $\Delta V_g$. The curves were calculated for gating efficiencies between ${\eta }_b/V_s=0$ (no bias voltage induced gating) and ${\eta }_b/V_s=-0.45{\mathrm{V}}^{\mathrm{-}\mathrm{1}}$. The peak value of $|g|$ increases with increasing ${\eta }_b/V_s$, whereas the linewidth decreases.

Figure 4

Maximal differential voltage gain $g_{\max }$ as a function of the bias voltage $V_{\mathrm{b}\mathrm{i}\mathrm{a}\mathrm{s}}$. The data extracted from the experiment ($★$) is plotted together with curves calculated for different gating efficiencies ${\eta }_b/V_s$. For ${\eta }_b/V_s=0$ (no bias induced gating) $g_{\max }$ is increasing linearly with $V_{\mathrm{b}\mathrm{i}\mathrm{a}\mathrm{s}}$. However, a nonlinear behavior was found for finite self-gating efficiencies (${\eta }_b/V_s<0$) in agreement with the experimental data.