Photoluminescence of Heterostructures with Ultrathin CdTe/ZnTe Quantum Wells
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Photoluminescence of Heterostructures with Ultrathin CdTe/ZnTe Quantum Wells N. G. Filosofova, A. Yu. Serova, G. Karczewskib, V. F. Agekyana, H. Mariettec, and V. P. Kochereshkod, * a
St. Petersburg State University, St. Petersburg, Russia Institute of Physics, Polish Academy of Sciences, Warsaw, Poland c Institut Neel CNRS, Grenoble, France d Ioffe Institute, Russian Academy of Sciences, St. Petersburg, Russia *e-mail: [email protected] b
Received March 26, 2020; revised March 26, 2020; accepted April 2, 2020
Abstract—Heterostructures of the CdTe/ZnTe type with ultrathin quantum wells are studied. Lines of light and heavy excitons bound to the CdTe layers are observed in the spectra. It is found that the photoluminescence intensity of the light exciton is comparable to the luminescence intensity of the heavy exciton. The temperature shifts of these lines are different, and the lines are intersected at a temperature of 65 K. The estimates of the energy and wave functions of the exciton states have made it possible to clarify parameters of some bands and excitons in such structures. Keywords: quantum wells, excitons, photoluminescence DOI: 10.1134/S1063783420090073
1. INTRODUCTION Semiconducting compounds of the A2B6 type, in particular, CdTe and ZnTe, are often used as model objects in fundamental studies. Their use in instrumental applications is negligible due to rapid degradation. At the same time, they often possess a high degree of structural perfection and unique optical properties. It would be nice to find a wider scope for their practical applications. The marked mismatch of crystal lattices is a reason that holds back the practical application of heterostructures based on these compounds. As a result, mechanical stresses that give rise to the degradation of the structure occur at the interfaces. This disadvantage is absent in heterostructures with ultrathin quantum wells, in which the crystal lattices are tuned to each other [1]. However, the band discontinuity value is known only approximately because of the lattice mismatch. Thus, the scatter of the published data on the band discontinuity value in the valence band of the CdTe/ZnTe heterostructures reaches ±10% of the total band discontinuity [2]. The situation is even worse with structures containing ultrathin (up to single atomic) layers. For such structures, the very concept of band discontinuity becomes vague [3]. The band discontinuity is comprised of the chemical band discontinuity determined by the chemical structure of the interface and the strain-induced band
discontinuity associated with the elastic energy at the interface of the contacting materials. According to the shared anion/cation rule, the band discontinuity in the valence band should be small in structures with a shared anion. Deformation can further reduce the band discontinuity and even can lead to the formation of a structure of type II for the holes. In this case, the Coulomb interaction with the electron becomes the most important factor in the quan
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