Thermally driven ballistic rectifier

The response of electric devices to an applied thermal gradient has, so far, been studied almost exclusively in two-terminal devices. Here we present measurements of the response to a thermal bias of a four-terminal, quasiballistic junction with a central scattering site. We find a novel transverse thermovoltage measured across isothermal contacts. Using a multiterminal scattering model extended to the weakly nonlinear voltage regime, we show that the device's response to a thermal bias can be predicted from its nonlinear response to an electric bias. Our approach forms a foundation for the discovery and understanding of advanced, nonlocal, thermoelectric phenomena that in the future may lead to novel thermoelectric device concepts.

Figure 1

(a) Schematic of the wafer structure with a 2DEG located in the GaInAs quantum well. (b) Schematic and scanning electron micrograph of a four-terminal antidot junction similar to the one reported on here. The four circles indicate connections to distant Ohmic contacts, not shown. The circuit diagram on the right shows the heating circuit used to heat the side channels; the configuration shown here is used to heat the right side channel. The lateral and transverse voltage drops are given by $V_{12}$ and $V_{34}$, respectively. The actual four-terminal junction measured here had terminal widths of $d_1\approx 500$ nm and $d_2\approx 450$ nm, and an antidot with a base and height of about 550 and 380 nm, respectively. The side heating channels are 5-$\mu$m wide, 30-$\mu$m long, and $\approx$4 $\mu$m from the scatterer. Note that the side channels are not to scale.

Figure 2

Main figure: First four harmonic transverse voltage responses to a temperature increase in terminal 1. The solid red line is a parabolic fit to the 2$\omega$ curve at low voltages, and is given by $V_{34}^{\left(2\omega \right)}=\left(1.9{\mathrm{V}}^{-1}\right)V_h^2$. Top inset: Schematic of the measurement configuration. Bottom inset: Measured lateral voltage drop across the junction during heating.

Figure 3

Main figure: First and second harmonic transverse responses, $V_{34}$, to a laterally applied 37 Hz voltage ${\nu }_{12}$. Also shown is a parabolic fit to the 2$\omega$ curve at low voltages. Inset: Circuit schematic for the applied voltage measurement.

Figure 4

$2\omega$ transverse response due to heating both side channels simultaneously and individually. The vertical dotted lines indicate the approximate onsets of nonlinear regimes.