Thickness-dependent strain relaxation and its role on exciton resonance energies of epitaxial ZnO layers grown on 6H-SiC substrates have been studied. The magnitudes of strain were determined experimentally by x-ray diffraction measurements. The strain ratios under biaxial stresses (Δc/c0)/(Δa/a0) of epitaxial ZnO layers grown on SiC and Al2O3 substrates were estimated to be 0.38 and 0.50, respectively. The strain-induced band shift δEA/δεzz for ZnO/SiC and ZnO/Al2O3 heterostructures was analyzed by photoluminescence with the values of 13.1 and 14.6 eV, respectively. These comparative strain-induced band shifts, as well as Poisson ratios, evidenced the role of lattice deformation kinetics induced by different lattice mismatches in the ZnO/SiC and ZnO/Al2O3 heterostructures.
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Ashrafi et al. (2004) studied this question.