Terahertz Photon-Assisted Tunneling in InAs Quantum Dots

Abstract

We have investigated electron transport in a single self-assembled InAs quantum dot (QD) coupled to nanogap metal electrodes under terahertz (THz) radiation. The fabricated QD samples operated as single electron transistors in a few electron regime, exhibiting clear shell structures. Under the THz radiation, in addition to the original Coulomb oscillation peaks, new side-peaks showed up. The dependence of the new side-peak current on the THz power follows the prediction of the photon-assisted tunneling (PAT) theory. Moreover, two types of PAT processes were observed in the THz range; the ground state resonance and the photon-induced excited state resonance, depending on the relative magnitude between the orbital quantization energy of the QDs and the THz photon energy. Furthermore, a very high coupling efficiency between the THz waves and the QDs was realized in our system and we observed multi-photon absorption up to the fourth-order during the tunneling process, resulting in almost complete lifting of the Coulomb blockade. This high coupling efficiency between THz wave and electrons in QDs opens a way to the manipulation of single electron charge/spin states in the THz frequency range.