Fine structure of excitons and polariton dispersion in quantum wells

Abstract

The fine structure of excitons, caused by the electron-hole exchange interaction, is modified in quantum wells due to the reduced symmetry and increased Coulomb interaction. We present a systematic formulation of the exchange interaction for quantum-well excitons and perform numerical calculations of the fine-structure splitting and dispersion for Alp. sGap. &As/GaAs quantum wells. The coupling of quantum-well excitons with the electromagnetic field is formulated in second quantization.By solving the coupled equations of motion for excitons and photons we calculate the dispersion relations for localized and resonant polaritons as well as the radiative lifetime for the resonant modes. Our results agree with those obtained by Andreani and Bassani [Phys. Rev. B 41, 7536 (1990)] and Tassone, Bassani, and Andreani [Nuovo Cimento D 12, 1673(1990], who used Maxwell's equations instead of the quantum field formulation. We draw some conclusions on the fine-structure splitting expected for excitons in quantum wells of II-VI semiconductors.

Long-range radiative interaction between semiconductor quantum dots

“…In what follows, the ω-dependence of the various quantities in the equations is implicitely contained in their k-dependence through Eqs. (5) and (6). In Eq.…”

“…(13). We compute these poles numerically within the exciton-pole approximation 4,5,6,7 , which consists in replacing the ω-dependence ofĜ αβ tensor by an average electron hole energyhω 0 . This approximation is generally valid when the dielectric medium does not present sharp resonances, as is the case in the present model where the QDs are embedded in a constant dielectric background.…”

“…In this case the importance of the coupling, expressed by the magnitude of the polariton self-energy correction to the bare exciton energy, is considerably smaller. In quantum wells 2,4,5,6,7 , the polariton resonance implies a finite exciton radiative lifetime which is of the order of 10 ps in typical GaAs quantum wells, and a negligible shift of the exciton energy. A similar effect is predicted in quantum wires 8,9,10 .…”

Exciton dephasing in ZnSe quantum wires

“…35 However, the radiative lifetime of the 11h transition in the SQW can be estimated to about 3 ps, 36 and is thus not the predominant dephasing mechanism even in the unpatterned structure. The influence of the decreased exciton-phonon scattering due to the reduced dimensionality, predicted in Refs.…”

From Localised to Ballistic Excitons in GaAs Quantum Wells

“…For p ol ari to ns the excito n and pho to n m odes are coupl ed whi ch m ay l ead to very hi gh gro up vel ociti es, as is evi denced by recent ti m e-of-Ûight experi m ents on mi cro cavi ti es [11]. The expected l i feti m e for p ol ari to ns i n G aAs QW s i s of the order of 40 ps [12], l eadi ng to an avera ge vel ocity of v p o l = R = §p o l ¤ 10 5 m/ s. Thi s val ue i s one order of m agnitude l ower tha n the p ol ari to n gro up vel ociti es measured i n m i crocavi ti es i n the experi m ent of Ref. [10], but at the same ti m e i t i s two orders of m agni tude hi g her tha n the bare excito n velo city for resona nt exci ta ti on.…”