Effects of substrate orientation on the optical anisotropy spectra of GaN/AlN/Si heterostructures in the energy range from 2 to 3.5 eV.

L.F. Lastras-Martínez, R.E. Balderas-Navarro, R. Herrera-Jasso, J. Ortega-Gallegos, A. Lastras-Martínez, Y. Cordier, J.-Ch. Moreno, E. Frayssinet, and F. Semond.
J. Appl. Phys. 111, 023511 (2012);, 2012.


We report reflectance (R) and reflectance difference spectroscopy (RDS) spectra of wurtzite heterostructures grown on Si(111) and Si(110) substrates in the energy range from 2.0 to 3.5 eV. Due to the threefold symmetry of the Si(111) surface, the heterostructures grown on this surface will relax isotropically through the formation of misfit dislocations, preferably at the AlN/Si interface, and no in-plane anisotropies are expected. In fact, only a small in-plane anisotropy of reflectance is observed, due to the initial residual off-cut of the silicon substrate that leads to wurtzite layers with a c-axis slightly tilted with respect to the surface. In contrast, for the Si(110) substrate, strong differences in lattice parameters appear between silicon and GaN/AlN depending on the considered in-plane direction, leading to a large in-plane anisotropy. By using a multiple reflection model for R and the in-plane anisotropies described, we developed a model to describe the RDS spectra in the vicinity and below the fundamental gap of GaN.