Excitons in asymmetric quantum wells

Abstract

Resonance dielectric response of excitons is studied for the high-quality GaAs/InGaAs heterostructures with wide asymmetric quantum wells (QWs). To highlight effects of the QW asymmetry, we have grown and studied several heterostructures with nominally square QWs as well as with triangle-like QWs. Several quantum confined exciton states are experimentally observed as narrow exciton resonances with various profiles. A standard approach for the phenomenological analysis of the profiles is generalized by introducing of different phase shifts for the light waves reflected from the QWs at different exciton resonances. Perfect agreement of the phenomenological fit to the experimentally observed exciton spectra for high-quality structures allowed us to obtain reliable parameters of the exciton resonances including the exciton transition energies, the radiative broadenings, and the phase shifts. A direct numerical solution of Schr\"{o}dinger equation for the heavy-hole excitons in asymmetric QWs is used for microscopic modeling of the exciton resonances. Remarkable agreement with the experiment is achieved when the effect of indium segregation during the heterostructure growth is taken into account. The segregation results in a modification of the potential profile, in particular, in an asymmetry of the nominally square QWs

Exciton-polariton interference controlled by electric field

“…In contemporary optical experiments with wide QWs in high-quality heterostructures, one can observe many quantum-confined exciton states. The states are typically observed as resonant features (oscillations) in the reflectance spectra of the heterostructures [40][41][42][43][44][45][46][47][48][49][50][51]. This allows one to study the effects of the external fields on the propagating excitons.…”

Inversion of Zeeman splitting of exciton states in InGaAs quantum wells

“…The layer thickness in all the samples has a gradient, therefore the actual width of the wide QWs (wider than 30 nm) was determined from the microscopic modeling of the exciton spectra (see details in Ref. [36]). For the points on the samples where the magnetic measurements were made, the fitted values of width are 87, 33, 40, and 45 nm for the 95-, 30-, 36-, and 41-nm QWs, respectively.…”

“…The strain induces a hh-lh splitting that results in a decrease of the hh-lh coupling compared to the unstrained material. Second, a segregation of indium atoms during the growth process changes the average width of the QW and breaks the presumed rectangular profile of the QW potential [36,44]. We account for this effect choosing an appropriate QW width to get good correspondence of the calculated exciton energy spectrum with that obtained experimentally.…”

Подавление Электронно-Дырочного Обменного Взаимодействия В Резервуаре Неизлучающих Экситонов

“…1. Наблюдаемые экситонные резонансы хорошо описываются в рамках стандартной модели отражения [3][4][5][6]. Это позволяет с высокой точностью определять спектральное положение и уширение экситонных резонансов.…”