Optical properties of cubic GaN from 1 to 20 eV

Abstract

We present a comprehensive overview of the optical properties of zinc-blende GaN. By a variety of different methods, such as temperature-dependent photoluminescence, photoluminescence excitation spectroscopy, photoreflectance, and ellipsometry, we investigate its emission and absorption related characteristics. The sample under study is a nearly strain-free epitaxial layer grown on freestanding cubic SiC. The light-hole/heavy-hole exciton was found at $3.271\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ at $5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, shifting to $3.208\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ at $295\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The split-off exciton transition was detected to be $21\phantom{\rule{0.222222em}{0ex}}\mathrm{meV}$ higher in energy. Taking the difference in the exciton binding energies into account, this yields a spin-orbit energy of ${\ensuremath{\Delta}}_{\mathrm{so}}=15\phantom{\rule{0.222222em}{0ex}}\phantom{\rule{0.222222em}{0ex}}\mathrm{meV}$. Donor and acceptor binding energies could be estimated by photoluminescence to be 30 and $130\phantom{\rule{0.222222em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{meV}$, respectively. By synchrotron-based spectroscopic ellipsometry the complex dielectric function up to an energy of $20\phantom{\rule{0.222222em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ could be determined. Comparison with ab initio calculations allows an assignment of high-energy features to the peculiarities of the band structure.