Photon Sidebands of the Ground State and First Excited State of a Quantum Dot

In analogy to spectroscopy on atoms it is interesting to study the interaction between light and electrons confined in quantum dots. However, since it is difficult to realize identical quantum dots the response of an ensemble of quantum dots to light excitation is strongly averaged over sample differences. Despite this averaging, excitation studies on quantum dot arrays by far-infrared light have shown the spectrum of collective modes [1], and inelastic light scattering experiments have probed single particle excitations [2]. The latter technique has also probed excitons in a single quantum dot [3]. We have used microwaves with relatively low frequency to study the discrete electron excitation spectrum in the conduction band of a single quantum dot. In contrast to the light transmission or luminescence measurements of the above spectroscopy techniques, we measure the photoresponse in the dc current. Current can flow through a quantum dot when a discrete energy state is aligned to the Fermi energies of the leads. This current is carried by resonant elastic tunneling of electrons between the leads and the dot. An additional time-varying potential e V coss2pftd can induce inelastic