Free excitons in wurtzite GaN - art. no. 115204

We present a comprehensive study of the free-exciton and exciton-polariton photoluminescence in wurtzite GaN. Using polarization-dependent measurement s we were able to resolve the fine-structure energy splittings in the n=1 s tate of the A exciton and to determine the energy separation between the 1S and 2P(+/-1) states as 19.7 +/-0.2 meV. For the n=1 state, the evolution o f the emission from two transverse polariton branches Gamma (5T1) and Gamma (5T2), the longitudinal exciton Gamma (5L), and the dipole-forbidden excit on Gamma (6) in magnetic fields up to 15 T have been studied in Faraday con figuration. We have estimated the value of the parallel effective g factor of the hole mixed into the 1 S state of the A exciton as g(A)(parallel to), 1S = 2.25 +/-0.2. To describe these data a theory is developed for the exci ton energy structure in hexagonal semiconductors with wurtzite symmetry in zero and in weak external magnetic fields which takes into account the effe ct of the hexagonal lattice anisotropy and the coupling of all excitonic st ates belonging to different valence subbands. The effect of the exciton int eraction with polar optical phonons is considered. The theory is very succe ssful in describing the free-exciton emission and magnetoluminescence in wu rtzite GaN. The effective mass parameters and the magnetic Luttinger consta nt as well as the effective Rydberg numbers and binding energies of the A, B, and C excitons are determined from a comparison of the theory with exper imental data.