An in-plane photoelectric effect in two-dimensional electron systems for terahertz detection

Abstract

The photoelectric effect consists in the photoexcitation of electrons above a potential barrier at a material interface and is exploited for photodetection over a wide frequency range. This three-dimensional process has an inherent inefficiency: photoexcited electrons gain momenta predominantly parallel to the interface, while to leave the material they have to move perpendicular to it. Here, we report on the discovery of an in-plane photoelectric effect occurring within a two-dimensional electron gas. In this purely quantum-mechanical, scattering-free process, photoelectron momenta are perfectly aligned with the desired direction of motion. The "work function" is artificially created and tunable in-situ. The phenomenon is utilized to build a direct terahertz detector, which yields a giant zero-bias photoresponse that exceeds the predictions by known mechanisms by more than 10-fold. This new aspect of light-matter interaction in two-dimensional systems paves the way towards a new class of highly efficient photodetectors covering the entire terahertz range.

Theory of the in-plane photoelectric effect in a two-dimensional electron system

“…In the experiment [16] the width of the 2D channel in the y-direction was macroscopically large (of the order of 1 µm) so that the number of occupied quasi-1D electron subbands E W n 2 was much larger than one. Under these conditions we can replace the sum over n in Eq.…”

“…Red arrows illustrate the momentum p of particles acquired under the action of the ac electric field of the incident wave: p is parallel to the surface but perpendicular to the potential step created by the gate voltages. (d) illustrates the photon absorption process; the Fermi level EF may lie above the both conduction band bottoms VL and VR; the maximum photocurrent efficiency is achieved when EF > VR [16].…”

“…Recently, a new type of the photoelectric effect, free from the mentioned drawbacks, has been discovered in Ref. [16]. In that paper a standard GaAs-AlGaAs heterostructure with a two-dimensional electron gas (2DEG) lying under the semiconductor surface has been used, Fig.…”

“…In Ref. [16] the lengths d, W , and b were equal d = 90 nm, W ≈ 0.7 µm, and b = 0.27 µm respectively. In the experiment [16] the two gates served as a bow-tie antenna of a complicated shape; here we will consider a simplified geometry with the gates having large dimensions (as compared to d, W , and b) both in x-and y-directions.…”

“…In the conventional photoelectric effect one of the chemical potentials is always negative, Figure 10(b), i.e., all electrons of the left material have energies below the potential barrier and have to absorb a photon to escape from the solid. A remarkable feature of the in-plane photoelectric effect [16] is that the photocurrent has a maximum when both chemical potentials are positive and the 2D gases are degenerate in both parts of the device, left and right from the materials interface. The maximum of the photocurrent function |J | is achieved in the point Figure 10 helps to understand the physical reason of this remarkable feature of the in-plane photoelectric effect.…”