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Magneto- and piezo-spectroscopy of high quality bulk samples have been used to clarify the origin of the characteristic, V1, V2 and V3 luminescence lines observed in 6H-SiC polytypes, correspondingly, at 1.433, 1.398, and 1.368 eV. The uniaxial stress, up to 500 MPa, was applied along [11-20] and [10-10] directions, perpendicular to the c-axis of the investigated 6H-SiC crystals. Magnetic field was applied in different directions with respect to the c-axis. The obtained results allow us to analyze in detail the symmetry of the initial and final states responsible for the V2 emission line. This analysis leads to a conclusion which contradicts the existing identification of the defect responsible for this characteristic emission. [ABSTRACT FROM AUTHOR]

Abstract: Different emission channels, due to recombination of neutral donor-bound excitons (D0X) in GaN, are discussed from photoluminescence experiments performed in magnetic fields up to 28T for a freestanding sample and a heteropepitaxial layer doped with silicon. For these samples, in addition to the principal recombination channel of D0X, 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 D0X transition have been observed. These effects are discussed in terms of resonant interaction between LO phonons and donor-bound electrons (magneto-polaron effect). [Copyright &y& Elsevier]

Luminescence experiments in magnetic fields up to 28 T on a freestanding gallium nitride (GaN) sample and a heteroepitaxial GaN layer lightly doped with silicon are presented. In these samples, the principal D0X recombination channel is accompanied by two electron satellites (TES), which involve the excited donor states as well as by the longitudinal-optic (LO) phonon replica of the principal transitions. When the internal donor excitations are magnetically tuned into resonance with the LO-phonon excitation, the intensity of TES is strongly enhanced and clear avoided-crossings between the LO-phonon replica of the principal D0X transition and TES involving highly excited states of oxygen and silicon are resolved. The observed behavior is explained in terms of resonant interaction between LO-phonons and donor-bound electrons. It is found that the resonant magnetopolaron interaction is stronger for the oxygen as compared to the silicon donor. [ABSTRACT FROM AUTHOR]