Adduced in this paper are the method and results of theoretical studying the effects of spatial confinement and exciton-phonon interaction on the position and shape of the excitonic absorption band in flat double nanoheterostructures GaAs/Al x Ga 1-x As. The heterojunction has been considered as unstrained, the nanosystem is modeled as a rectangular quantum well of a finite depth. Interaction of exciton with optical polarization phonons has been taken into account. Calculated has been the temperature dependence of the energy corresponding to transition into the background excitonic state, and determined have been temperature changes in the absorption coefficient related with this transition. It has been shown that observation of these temperature changes in the energy and absorption coefficient, caused by interaction with optical phonons, is possible in the case of exciton with heavy hole at temperatures above 100 K.

Abstract. Using approximation of dielectric continuum and the Green function method, studied in this work is the influence of electron-phonon interaction on position of the bottom of the ground energy band for electron in the quantum well of a finite depth. Considering the example of a plain nano-heterostructure with a quantum well based on the double heterojunction Al x Ga 1-x As/GaAs (nanofilm), the authors have calculated the electron energy for a varied thickness of the film. It has been studied the influence of barrier material composition as well as electron-phonon interaction on the electron energy.

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The energy of transition into the ground excitonic state for a quasi-two-dimensional (nanofilm) semiconductor nanoheterostructure with single quantum well and its dependences on the thickness, temperature, and composition of the barrier medium are calculated in the dielectric continuum approximation using the Green's function method. Specific calculations are made for a nanofilm containing a rectangular finite-depth quantum well created by the double heterojunction GaAs/Al𝑥Ga1−𝑥As taken as an example. For the films narrower than 30-40 nm, the transition energy is shown to be mainly governed by the confinement effect and the aluminum content 𝑥. In particular, the energy decreases rapidly from 1.55 eV (at 𝑥 = 0.2), 1.62 eV (at 𝑥 = 0.3), or 1.69 eV (at 𝑥 = 0.4) to 1.41 eV for all those 𝑥-values, as the film thickness grows. The further increase in the film thickness up to approximately 100 nm is accompanied by a slow growth of the energy to the value characteristic of bulk GaAs, which occurs due to the corresponding reduction in the exciton binding energy. The rate of this growth depends weakly on 𝑥. The temperature increase from 0 to 300 K results in a long-wave shift of the exciton band bottom. As a result, the transition energy decreases by a value weakly depending on the film thickness and ranging from 2 meV at 𝑥 = 0.2 to 3 meV at 𝑥 = 0.4. The temperature-induced variations are invoked by the interaction with phonons, which are mostly confined ones in nanofilms thicker than 30-40 nm or interface ones, if nanofilms are thinner. K e y w o r d s: nanoheterostructure, quantum well, exciton, exciton-phonon coupling.

The results of theoretical study of the temperature dependence of a long-wave range fundamental absorption edge in flat nanoheterostructures with a single quantum well (nanofilms) are adduced. The quantum well is assumed to be rectangular, of finite depth, and with unstrained heterojunctions as the nanofilm surface. Energies of electrons, holes, and excitons have been calculated within the framework of the effective mass model using the Green functions techniques, with account of their interaction with polar optical phonons confined within a quantum well. Numerical calculations are performed for nanofilms β-CdS/β-HgS/β-CdS and Al_0.3Ga_0.7As/GaAs/Al_0.3Ga_0.7As. It is shown that interaction with optical phonons causes a long-wave shift of the threshold frequency of the fundamental absorption band and a shift of exciton peaks by hundreds of Å for the first mentioned nanofilm and by dozens of Å for the second one, which is characterized by lower magnitudes of the constants of the electron-phonon coupling. The shift magnitude, as well as the height and half-width of the exciton absorption band, changes when the temperature exceeds 80 and 100 K, respectively.