Christopoulos, S.von Hogersthal, G. B. H.Grundy, A. J. D.Lagoudakis, P. G.Kavokin, A. V.Baumberg, J. J.Christmann, G.Butte, R.Feltin, E.Carlin, J. F.Grandjean, N.2010-10-052010-10-052010-10-05200710.1103/PhysRevLett.98.126405https://infoscience.epfl.ch/handle/20.500.14299/55055WOS:000245135400043We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 mu J cm(-2), 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/- 5 degrees and spatial size around 5 mu m.SPONTANEOUS-EMISSIONCONTINUOUS-WAVEGANLASERSEXCITATIONtext::journal::journal article::research article