Room-temperature transport of indirect excitons in (Al,Ga)N/GaN quantum   wells
  We report on the exciton propagation in polar (Al,Ga)N/GaN quantum wells over several micrometers and up to room temperature. The key ingredient to achieve this result is the crystalline quality of GaN quantum wells (QWs) grown on GaN template substrate. By comparing microphotoluminescence images of two identical QWs grown on sapphire and on GaN, we reveal the twofold role played by GaN substrate in the transport of excitons. First, the lower threading dislocation densities in such structures yield higher exciton radiative efficiency, thus limiting nonradiative losses of propagating excitons. Second, the absence of the dielectric mismatch between the substrate and the epilayer strongly limits the photon guiding effect in the plane of the structure,making exciton transport easier to distinguish from photon propagation. Our results pave the way towards room-temperature gate-controlled exciton transport in wide-bandgap polar heterostructures. 
F. Fedichkin, T. Guillet, P. Valvin, B. Jouault, C. Brimont, T.   Bretagnon, L. Lahourcade, N. Grandjean, P. Lefebvre, M. Vl...
cond-mat.mes-hall cond-mat.quant-gas