Fröhlich interaction in InAs/GaAs self-assembled quantum dots

Abstract

The phonon bottleneck in self-assembled InAs/GaAs quantum dots ͑SAD's͒ is observed directly in continuous-wave photoluminescence experiments when exciting one GaAs longitudinal optical ͑LO͒-phonon energy above the ground level of the smallest dot. To overcome the phonon bottleneck, selective photoluminescence ͑PL͒ experiments are performed and multiple phonon-assisted radiative bands are observed. We found that no real crystal states are involved in the experimentally observed phonon emission. Under nonresonant excitation at 5 K, the SAD's photoluminescence band is centered at 1.315 eV. As proven by our photoluminescence experiments at high excitation densities, there are no excited states in such small dots. We interpret the phonon-assisted PL as being due to enhanced Fröhlich interaction between strain-induced polarized excitons in the SAD's and LO phonons. Further experimental support for this model is found from the cleaved-side PL measurements. A light-hole ground state is observed, instead of the theoretically predicted heavy-hole one.

Enhanced phonon-assisted photoluminescence in InAs/GaAs parallelepiped quantum dots

“…7,8 Recently, the observed photoluminescence spectra in InAs/GaAs self-assembled quantum dots were attributed to a giant efficiency of the Fröhlich interaction between a strain-induced polarized exciton and the longitudinal optical ͑LO͒ phonons. 9 In nanostructures where the motion of charge carriers is confined to a small volume, the efficiency of the phonon-assisted interband transition processes greatly increases in the regime of strong size quantization, l рR B , where l is a characteristic size of a nanostructure and R B is the exciton Bohr radius. In bulk InAs, the electron-phonon interaction is very weak: the Fröhlich coupling constant is ␣ InAs Ϸ0.052.…”

Photoluminescence of small-size semiconductor quantum dots

“…Indeed, typical transition energies of such type of quantum dots reported in literature are 1.0-1.2 eV for the lowest exciton state. As reported in [16], the edge of the wetting layer (WL) in this system is around 1.35 eV. No PL from WL was observed indicating very efficient and rapid capture of photocreated carriers into quantum dots.…”

“…The investigated InAs/GaAs quantum dots were grown by molecular beam epitaxy of InAs in an amount equivalent to 2.0 monolayers (ML) on a (001) oriented GaAs substrate [16]. The InAs/GaAs QD samples were provided via P.M. Koenraad of the Physics Department of the TU Eindhoven (The Netherlands).…”

Запрещенное резонансное комбинационное рассеяние света в сверхрешетках GaAs/AlAs: эксперимент и расчеты

“…Видны широкие полосы сигналов в красном диапазоне (по-видимому, от прямых переходов) и на границе инфракрасного диапазона. В случае такой короткопе-риодной сверхрешетки энергии прямых оптических пе-реходов выше, чем непрямых [31]. Вероятно, полоса фотолюминесценции на границе инфракрасного диапа-зона обусловлена непрямыми переходами.…”

“…Мы рассчитали собственные частоты и собственные векторы, а также электриче-ский дипольный момент этих 84 мод для волнового вектора 10 6 см −1 вдоль осей Z, X ′ и X. В работе [28] было предположено, что моды с большими дипольными моментами могут взаимодействовать с заряженными частицами (электронами или дырками) в сверхрешет-ках за счет кулоновского взаимодействия. В более об-щем случае кулоновский механизм электрон-фононного взаимодействия известен как фрёлиховский механизм, проявляющийся в транспортных явлениях, а также в комбинационном рассеянии света [3,[24][25][26][27][28][29][30][31]. Интенсив-ность фрёлиховского рассеяния обычно пропорциональ-на квадрату волнового вектора, его часто связывают с квадрупольным механизмом [24].…”