Hole-hole and electron-hole exchange interactions in single InAs/GaAs quantum dots

Abstract

A combined analysis of microphotoluminescence ͑PL͒ and microphotoluminescence excitation ͑PLE͒ spectra of the same single quantum dot ͑QD͒ enables an unambiguous identification of four sharp resonances in the excitation spectrum detected on the positive trion transition ͑h 0 → e 0 h 0 h 1 ͒ and reveals the complete fine structure of the hot trion. Transitions into states normally forbidden by ͑spin͒ selection rules for optical transitions between pure spin states are observed. The splittings of all triplet states are found to be large ͑up to 3 meV͒, asymmetric, and QD size and shape dependent. The experimental data are in excellent agreement with theoretical calculations in the framework of eight-band k · p theory and the configuration-interaction method. To account for the physical effects which lead to the observed fine-structure splitting, parts of the complex model are successively omitted. This approach identifies the anisotropic hole-hole exchange interaction as well as correlation effects dominating the observed fine-structure splitting of the hot trion.

Accurate defect levels obtained from the HSE06 range-separated hybrid functional

“…7 Until now, however, studies of the FSS of neutral and charged exciton complexes have been limited to QDs of C 2v or lower symmetry. [2][3][4][5][6][7][8][9][10][11] In this Rapid Communication, we experimentally and theoretically investigate the FSS in QDs with high symmetry. Zincblende QDs of C 3v symmetry can ideally be achieved by choosing ͓111͔ as the crystallographic direction of crystal growth instead of the conventional ͓001͔ direction.…”

Origin of two-hole triplet splitting in circular quantum dots

“…That involving T 0 gives rise to transitions C and D, and that involving T * ± gives rise to transition E. It is worth noticing that the resonances corresponding to transitions B-E are non-degenerate, contrary to the spectrum expected from single-band models, and is consistent with optical measurements of positive trions, which reveal various resonances under the fundamental transition. [6,7,8] Note also that C and D resonances differ only in the final hole state, so their splitting provides a direct measurement of the p-shell splitting, ∆ 0 . Yet, this resonance may be difficult to observe experimentally because T 0 tends to thermalize quickly to the singlet ground state.…”

“…[1,4] The same fine structure was expected for positive trions, [5] but recent optical measurements reveal the presence of an additional number of resonances and large (∼ meV) splittings, which cannot be accounted for by the weak electron-hole exchange interaction alone. [6,7,8] Warming and co-workers showed that these splittings could be correctly reproduced if one considers anisotropic hole-hole exchange interaction and Coulomb correlations. [6] The underlying idea is that piezoelectric fields lower the otherwise circular symmetry of self-assembled InAs/GaAs QDs.…”

“…[6,7,8] Warming and co-workers showed that these splittings could be correctly reproduced if one considers anisotropic hole-hole exchange interaction and Coulomb correlations. [6] The underlying idea is that piezoelectric fields lower the otherwise circular symmetry of self-assembled InAs/GaAs QDs. Because the valence band spin-orbit interaction is significant, the hole-hole spin exchange interaction is sensitive to the spatial asymmetry and hence degeneracies are lifted.…”

“…We next show this pshell splitting gives rise to a non-negligible splitting of the two-hole triplet, which is clearly reflected in the optical spectrum of hot trions, as noted in related experiments. [6,7,8] Because HH-LH coupling is so influential in these systems, we also investigate whether it has a significant impact on the spin purity of the hot trion, which could affect the performance of positive trions in practical applications. [7] We find that the spin purity of the excited triplet rapidly decreases with increasing aspect ratio, but that of the singlet remains high.…”