Biaxial strain effect in exciton resonance energies of epitaxial ZnO layers grown on 6H-SiC substrates

Thickness-dependent biaxial strain relaxation of epitaxial ZnO layers grown on 6H-SiC substrates has been addressed. The strain ratio under the biaxial stress was estimated to be 0.38, while the c/a ratio changed from 1.593 to 1.608. The biaxial strain was accounted maximum for the ZnO layer thickness of >= 6->= 200 nm. Free (FXA), donor-bound ((DX)-X-0), and neutral acceptor-bound (A(0)X) excitons energies were blue shifted with the increase of layer thickness to be 2.5, 4.8, and 5.8 meV, respectively. The strain-induced band shift for the FXA, FXB, and (DX)-X-0 bands was estimated with the corresponding energies of 13.1, 16.4, and 14.6 eV. The strain-induced optical band structure was analyzed using the Hamiltonian for the valence bands under the out-of-plane biaxial strain. (C) 2004 Published by Elsevier B.V.