Impact of band structure and transition matrix elements on polarization properties of the photoluminescence of semipolar and nonpolar InGaN quantum wells
L. Schade1,2, U.T. Schwarz1,2, T. Wernicke3, M. Weyers4, and M. Kneissl3,4
Published in:
phys. stat. sol. (b), vol. 248, no. 3, pp. 638-646 (2011).
Abstract:
Partial or full linear polarization is characteristic for the spontaneous emission of light from semipolar and nonpolar InGaN quantum wells. This property is an implication of the crystalline anisotropy as a basic property of the wurtzite structure. The influence of this anisotropy on the band structure and the transition matrix elements was calculated by a k · p-method for arbitrary quantum well orientations with respect to the c-axis; results are shown here in detail. Optical polarization is a direct consequence of a broken symmetry, mainly affecting the transition matrix elements from the conduction to the valence bands. Furthermore, the strain of the InGaN quantum well strongly depends on the crystal orientation of the substrate, resulting in a valence band mixing. The composition of the eigenfunctions has emerged to be most important for the polarization dependence of strained semipolar and nonpolar InGaN QW. The matrix elements, in combination with the thermal occupation of the bands, determine the polarization of the spontaneously emitted light. Our photoluminescence measurements of nonpolar QW match well with this model. However, in contrast to calculations with standard band parameters, the two topmost subbands show a larger separation in the emitted energy.
1 Department of Microsystems Engineering, University of Freiburg, Georges-Köhler-Allee 103, 79108 Freiburg, Germany
2 Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastraße 72, 79108 Freiburg, Germany
3 Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin, Germany
4 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
Keywords:
band structure, InGaN, k·p approximation, polarization, photoluminescence, quantum wells
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