Rectification in Mesoscopic Systems with Broken Symmetry: Quasiclassical Ballistic Versus Classical Transport

In suitably designed mesoscopic semiconductor structures, the phenomenon of ballistic rectification can be observed. A currently discussed microscopic model relates the observations to the interplay between fully quantized and quasiclassical current paths. We present measurements that contribute substantially to the clarification of the fascinating topic. In particular, we observe the opposite sign of the output voltage as compared to the prediction. Demonstrating the basic principle upon which the rectification is based—the asymmetry of the voltage drop in a quasiclassical wire—and extending the model to the classical transport regime, we can well explain our experiments as being caused by the interplay of quasiclassical ballistic and classical transport. Tunable ballistic rectifiers generating very large output signals and operating at room temperature raise the hope for future applications.

Figure 1

$I\mathrm{\text{−}}V$ curves of a device combining 150 nm and $3\mu \mathrm{m}$ wide leads for different gate voltages at 4.2 K. If the gate voltage is sufficiently low, strong nonlinear effects can be observed, and the external current is rectified. The inset is an atomic force micrograph of the active part of the sample, illustrating the geometry and the labeling of the contacts.

Figure 2

Determination of the chemical potential of a voltage probe $P$ that is connected by identical leads to a source contact $S$ and a drain contact $D$ for different channel widths. The central parts of the devices are shown in the insets. (a) In the case of a $3\mu \mathrm{m}$ wide channel, the source-drain voltage drops symmetrically as expected for a classical conductor. (b) In the case of a 300 nm wide channel, the potential of the voltage probe is shifted towards that of the negatively biased reservoir. Compared to (a), the chemical potential ${\mu }_P$ is raised, corresponding to quasiclassical behavior.

Figure 3

Transverse current-voltage characteristics of a tunable ballistic rectifier for four equivalent gate configurations. The basic layout of the device and the operating principle of the in-plane gates are schematically illustrated in the insets. Whenever the gate-induced asymmetry is sufficiently large, rectification can be observed. In the experiments shown in the upper left and the lower right, the external current is injected into contact 2 and drawn out at contact 4, and the rectified voltage is measured between the contacts 1 and 3. In the other two measurements, current and voltage contacts are exchanged. Comparing the diagonally opposing curves, one can see that a reversal of the channel widths results in a reversal of the output signal.