The Editor's Choice article “Analysis of polarization-dependent photoreflectance studies for c -plane GaN films grown on a -plane sapphire” by M. Röppischer et al. (pp. 773–779) was selected among the contributions from the 3rd International Workshop on Modulation Spectroscopy of Semiconductor Structures (MS3) presented in this issue of physica status solidi (a).
In the paper the optical properties of c -plane GaN layers grown on a -plane sapphire are investigated through the combination of experimental measurements and the calculation of transition energies and oscillator strengths. The front cover picture shows the calculated exciton transition energies at the center of the Brillouin zone for room temperature as well as the differences between them. The picture also illustrates the strain component parallel to the c-axis as a function of the in-plane strain. One can deduce from the upper three diagrams that the transition energies increase for net compressive strain, while they decrease for tensile strain. In addition, the diagrams are symmetric by the isotropic strain line, so one can exchange the values of strain for x- and y-components, and the same transition energies are obtained. The measured photoreflectance signals of c-plane GaN on a-plane sapphire are well described by the calculated transition energies in connection with the oscillator strength (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)