Optical emission from a charge-tunable quantum ring

Abstract

Quantum dots or rings are artificial nanometre-sized clusters that confine electrons in all three directions. They can be fabricated in a semiconductor system by embedding an island of low-bandgap material in a sea of material with a higher bandgap. Quantum dots are often referred to as artificial atoms because, when filled sequentially with electrons, the charging energies are pronounced for particular electron numbers; this is analogous to Hund's rules in atomic physics. But semiconductors also have a valence band with strong optical transitions to the conduction band. These transitions are the basis for the application of quantum dots as laser emitters, storage devices and fluorescence markers. Here we report how the optical emission (photoluminescence) of a single quantum ring changes as electrons are added one-by-one. We find that the emission energy changes abruptly whenever an electron is added to the artificial atom, and that the sizes of the jumps reveal a shell structure.

Energy spectra of quantum rings

“…The phase coherence of transport through a quantum dot embedded in one arm of an open ring has been demonstrated [4]. The energy spectrum of closed rings [5] has only recently been analysed by optical experiments [6,7] and is the basis for the prediction of persistent currents [8] and related experiments [9-11]. Here we report magnetotransport experiments on a ring-shaped semiconductor quantum dot in the Coulomb blockade regime [12].…”

Exciton Fine-Structure Splitting in Self-Assembled Lateral InAs/GaAs Quantum-Dot Molecular Structures

“…The spectral linewidth of ~15-35 µeV is in agreement with previous studies of QMSs. [23][24][25] We note that this linewidth is much larger than what is expected from the lifetime broadening or the spectral resolution of our instrument (~5 µeV). We believe that the main reason for the observed inhomogeneous broadening of the PL linewidth is the random fluctuations of local potentials as a result of e.g.…”

Spin-Dependent Coupling of Charged Quantum Dot Excitons with Continuum States

“…This model can be justified by the (395) shell structure observed when a quantum dot is filled either with excitons [1] or with electrons [2]. At low temperature, the artificial atom picture is strengthened by the long coherence times of an exciton in a quantum dot [3][4][5], motivating the application of quantum dots in quantum optics and quantum information processing.…”

“…We do this by adding excess electrons to the neutral exciton X 0 to create the singly charged exciton X 1− (trion), the doubly charged exciton X 2− and the triply charged exciton X 3− . We employ quantum dots embedded in a field-effect structure that allows us to control precisely the charge of the exciton [2]. In these experiments, a hole is generated with optical excitation.…”

“…In these experiments, a hole is generated with optical excitation. Over large regions of bias voltage, the excitonic charge is constant, and there are abrupt steps in emission energy whenever an additional electron is added to the dot [2]. The sample is grown on a GaAs substrate, on which a buffer layer, an n + -GaAs layer (the back contact) and then a 25 nm thick undoped GaAs layer (the tunnel barrier) are grown.…”