Magneto-spectroscopy of donor-bound excitons in GaN

Different emission channels, due to recombination of neutral donor-bound excitons ((DX)-X-0) in GaN, are discussed from photoluminescence experiments performed in magnetic fields up to 28 T for a freestanding sample and a heteropepitaxial layer doped with silicon. For these samples, in addition to the principal recombination channel of (DX)-X-0, in which donors are left in their ground states, the well-resolved two-electron satellites (TES) involving different donor excitations were observed. A detailed analysis of the magneto-optical data provides important knowledge about the energy structure of the oxygen and silicon donors in wurtzite GaN. The application of high magnetic fields allowed us to tune the intra-donor excitations across the LO-phonon energy. A strong enhancement of TES intensity and the appearance of several anti-crossing processes in the vicinity of the LO-phonon replica of the principal (DX)-X-0 transition have been observed. These effects are discussed in terms of resonant interaction between LO phonons and donor-bound electrons (magneto-polaron effect). (C) 2007 Elsevier B.V. All rights reserved.