Eur. Phys. J. B (2013) 86: 59
https://doi.org/10.1140/epjb/e2012-30558-3

Regular Article

Computation of the electronic structure and direct-gap absorption spectra in Ge-rich Si_1−x Ge_x/Ge/Si_1−xGe_x type-I quantum wells

¹ Laboratoire de la Matière Condensée et des Nanosciences (LMCN), Département de Physique, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir, Tunisie
² Centre Interdisciplinaire de Nanoscience de Marseille (CINaM), UMR CNRS 7325 – Université Aix-Marseille, Case 913, Campus de Luminy, 13288 Marseille cedex 9, France
³ Institut d’Electronique Fondamentale, Université Paris-Sud, CNRS, 91405 Orsay, France

^a Present address: Materials Technology Unit, Qatar University, 2713 Doha, Qatar.
^b e-mail: sfinafsm@yahoo.fr
^c e-mail: moncefsaid@yahoo.fr

Received: 6 July 2012
Received in final form: 6 November 2012
Published online: 18 February 2013

Abstract

This paper presents the results of conduction band discontinuities calculation for strained/relaxed Si_1−xGe_x/Si_1−yGe_y heterointerfaces in Γ_15C, Γ_2′C and L upper bands minima, as well as the room-temperature strained (vs. relaxed) band gaps deduced from the classical model-solid theory. Based upon the obtained data, we propose a type-I W-like Si_1−yGe_y/Si_1−xGe_x/Ge/Si_1−xGe_x/Si_1−yGe_y quantum wells heterostructure optimized in terms of compositions and thicknesses. Electronic states and wave functions are found by solving Schrödinger equation without and under applied bias voltage. An accurate investigation of the optical properties of this heterostructure is done by calculating the energies of the interband transitions and their oscillator strengths. Moreover, a detailed computation of the bias-voltage evolution of the absorption spectra is presented. These calculations prove the existence of type-I band alignment at Γ_2′C point in compressively strained Ge quantum wells grown on relaxed Ge-rich Si_1−yGe_y buffers. The strong absorption coefficient (> 8 × 10³ cm^-1) and the large Stark effect (0.1 eV @ 2 V) of the Γ_2′C transitions thresholds open up perspectives for application of these heterostructures for near-infrared optical modulators.