Photon-Assisted Tunneling through a Quantum Dot

Abstract

It is now possible to confine electrons in all three dimensions in semiconductors, resulting in the formation of what is commonly called a quantum dot. Electrons in these dots exhibit striking classical and quantum effects. Because of their small size, quantum dots have low capacitance C, which leads to a non-negligible electrostatic energy change upon addition or subtraction of an electron from a dot. This energy e 2 /C, typically 0.5 meV, suppresses fluctuations in electron number, allowing for the controlled addition of electrons to the dot by applying a voltage to a gate electrode. Measuring the current through the dot as a function of this gate voltage results in observation of highly regular current peaks, the so-called classical Coulomb Blockade oscillations. As the electrons are completely localized, the energy spacing between levels in a dot may also be relevant. If this energy Δε is comparable to e 2 /C, features may be present in the current due to these so-called 0D states. The interplay between the classical Coulomb Blockade and the quantum states of a dot has been extensively studied by dc transport measurements [1].