Temperature changes in the function of the shape inherent to the band of exciton absorption in nanofilm of layered semiconductor

Abstract

Abstract. Represented in this paper is the method and results of theoretical investigations aimed at the influence of spatial confinement effects, self-polarization of heterojunction planes as well as exciton-phonon interaction on the position and shape of the band corresponding to exciton absorption in nanofilms of layered semiconductor in a dielectric matrix. The heterojunction is considered as unloaded, the nanosystem is modeled by an infinitely deep quantum well and characterized by an essential difference between dielectric permittivities on both sides of the heterojunction. Calculated in this work are the dependences for the form-function of the absorption band on the thickness of lead iodide nanofilm embedded into polymer E-MAA or glass, and on its temperature. The results of calculations are in good accordance with known data of experimental measurements.

Temperature changes in the exciton absorption band observed in flat double nanoheterostructures GaAs/AlxGa1-xAs

“…The mass operator (4) defines influence of excitonphonon interaction (EPI) on the exciton energy spectrum in the system, position and width of the exciton absorption band. To find it, EPI Hamiltonian can be represented in the following form (6) and it is defined here for the case of interaction with confined phonons in infinitely deep QW, like to that adduced in [26]. It can be also used for QW of a finite depth if assuming a respective change in the look of the function for electron-phonon coupling…”

“…Using the EPI function defined in this manner, in accord to [26] we find the one-phonon mass operator that takes into account interaction of the background exciton state with confined phonons and obtain the explicit form of its real (8) parts. Here, a 0 and ε 0 are the lattice parameter and static dielectric permittivity of well material, respectively; N = a/a 0 is the number of well material layers in NF with the thickness a;…”

“…calculated without account of EPI; Γ 0phenomenological constant taking into account relaxation of excitons caused by processes non-included to the accepted model. The rest auxiliary values and functions in Exps (7) and (8) were earlier adduced in [26].…”

Frequency spectrum and group velocities of acoustic phonons in PbI2 nanofilms

“…As a result, a number of works have been published in recent years, in which the results of both experimental and theoretical studies of various properties of ultrathin films of lead iodide are presented. In particular, the structure of the phonon spectrum and regularities of the heat transfer phenomenon were studied in works [5][6][7], and the transformation of the energy spectrum of the electronic system due to its interaction with optical phonons and changes in the exciton absorption band in such structures were studied in works [8][9][10].…”

“…To construct dispersion curves in such structures, numerical calculations are usually used (see, for example, [11,12]), and when calculating quantities that characterize a phenomenon or process, are limited to regularities valid for bulk (three-dimensional) crystals. However, to consistently describe the electron-phonon interaction, it is Frequency Spectrum and Group Velocities of Acoustic Phonons in PbI2 Nanofilms 479 necessary to use functions that describe the dispersion dependences for all branches of the phonon spectrum (see, for example, [8][9][10]13]). Thus, the problem of establishing such functions is relevant for the development of the theory of electron-phonon interaction in nanostructures.…”