Quasi-one-dimensional density of states in a single quantum ring

Abstract

Generally confinement size is considered to determine the dimensionality of nanostructures. While the exciton Bohr radius is used as a criterion to define either weak or strong confinement in optical experiments, the binding energy of confined excitons is difficult to measure experimentally. One alternative is to use the temperature dependence of the radiative recombination time, which has been employed previously in quantum wells and quantum wires. A one-dimensional loop structure is often assumed to model quantum rings, but this approximation ceases to be valid when the rim width becomes comparable to the ring radius. We have evaluated the density of states in a single quantum ring by measuring the temperature dependence of the radiative recombination of excitons, where the photoluminescence decay time as a function of temperature was calibrated by using the low temperature integrated intensity and linewidth. We conclude that the quasi-continuous finely-spaced levels arising from the rotation energy give rise to a quasi-one-dimensional density of states, as long as the confined exciton is allowed to rotate around the opening of the anisotropic ring structure, which has a finite rim width.

Excitonic Aharonov–Bohm Oscillations in Core–Shell Nanowires

“…Figures b,c show photoluminescence spectra taken on two different single nanowires (NW1 and NW2, respectively) at 4.2 K. The transition energies indicate shell quantum wells with a width of t = 7 nm. The full width at half maximum of these lines is typically between 200 and 500 µeV, smaller than reported for GaAs crystal‐phase quantum wells, larger than those of crystal‐phase quantum dots, and comparable to those reported for GaAs‐based quantum wires obtained by post‐growth lithography techniques . Hence, we attribute the narrow transitions in the spectra to single quantum rings.…”

Modeling Quantum Beats by Degenerate Four‐Wave Mixing Spectroscopy in a Single GaAs/AlGaAs Quantum Ring

“…The center energy of a picosecond laser spectrum is tuned near l = 3 state with moderate excitation of a pulse area ( Θ = 0.36 π ), and up to seven different states ( l = 0–6) are excited coherently. Provided that PL spectrum appears near 1.695 eV in a single GaAs/AlGaAs QR, this can be attributed to a ring‐like wavefunction . Therefore, the central laser energy ( ħω c ) of a picosecond pulse can be tuned with respect to the ground state PL (0,0) in the absence of B by using the detuning energy (Δ E = ħω − ħω c ).…”

Physics of Quantum Rings

“…Progress in epitaxial techniques in recent decades has resulted in burgeoning developments in the physics of quantum dots (QDs), i.e., semiconductor-based 'artificial atoms'. More recently, a lot of attention has been turned towards non-simplyconnected nanostructures, such as quantum rings (QRs), which have been obtained in various semiconductor systems [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. Originally, QRs were fabricated accidently, when optimizing growth conditions for self-assembled InAs quantum dots on a GaAs substrate, the QD material was splashed out from the QD centre, forming a volcano-like structure [6,7,8,9].…”

“…Originally, QRs were fabricated accidently, when optimizing growth conditions for self-assembled InAs quantum dots on a GaAs substrate, the QD material was splashed out from the QD centre, forming a volcano-like structure [6,7,8,9]. Improved and perfected, it has now become a routine procedure for the fabrication of QRs with typical radii of 10 100nm [11,12,13,14,16,18,19,21,22,23,24,25,26,27,28,29,30]. In the literature, QRs produced as described above are usually referred to as 'type-I quantum rings'.…”