Optical anisotropy of InAs/GaSb broken-gap quantum wells

Abstract

General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. ISSN 1063 7761, Journal of Experimental and Theoretical Physics, 2012, Vol. 114, No. 5, pp. 731-737. © Pleiades Publishing, Inc., 2012 731 1 INTRODUCTIONThe knowledge on optical properties of broken gap heterostructures with InAs/GaSb or similar quantum wells is of great importance because of intensive exper imental investigations on the application of these structures for infrared laser generation. Cascade lasers with multiple quantum wells have been proposed [1] and realized experimentally [2][3][4]. The active region of these devices can contain more than ten stages con sisting of InAs, GaSb, AlSb or other (for example, GaInSb or AlInSb) thin layers. The narrow gap InAs and GaSb layers have two dimensional electron and hole levels between which the optical transitions occur. The wide gap AlSb (AlGaSb, AlInSb) tunnel ing barriers supply the transfer of the carriers through the structure to achieve the population inversion between the electronlike and hole like levels and the laser generation. It was shown that such a laser can operate at temperatures up to 100 K [4].In cascade lasers, the first electron like level in the InAs layer 1e is higher than the first heavy hole like level 1hh in the GaSb layer [5,6]. The separation between them corresponds to the mid infrared energy range for the emitted photons. However, the situation can be different for quantum wells with thicker InAs and GaSb layers. Because of an overlap of the InAs conduction band and the GaSb valence band, the 1e 1 The article is published in the original. level can then be located below the 1hh level at the zone center (with the carrier in plane wave vector k || = 0) [5]. The 1e and 1hh levels anticross and hybridize for k || ≠ 0, which has been observed experimentally [7,8] and studied theoretically [5,[9][10][11]. Laser genera tion in such thicker structures with hybridized elec tron hole states has been also proposed [8]. In this case, the optical transitions exist between the states of the second electron like subband 2e in the InAs layer and the lower hybridized states. These hybridizations can occur between two states (one electron state and one heavy hole state or one electron state and one light hole state). Also, three states (an electron state, a heavy h...