@Article{Fernandez-Garrido_prappl_2016,
  Title                    = {Comparison of the Luminous Efficiencies of {Ga-} and {N-}Polar ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1-x}\mathrm{N}/{\mathrm{In}}_{y}{\mathrm{Ga}}_{1-y}\mathrm{N}$ Quantum Wells Grown by Plasma-Assisted Molecular Beam Epitaxy},
  Author                   = {Fern\'andez-Garrido, Sergio and L\"ahnemann, Jonas and Hauswald, Christian and Korytov, Maxim and Albrecht, Martin and Ch\`eze, Caroline and Skierbiszewski, Czes\l{}aw and Brandt, Oliver},
  Journal                  = {Phys. Rev. Applied},
  Volume                   = {6},
  Pages                    = {034017},
  Year                     = {2016},
  Abstract                 = {We investigate the luminescence of Ga- and N-polar InxGa1−xN/InyGa1−yN quantum wells grown by plasma-assisted molecular beam epitaxy on freestanding GaN as well as 6H-SiC substrates. In striking contrast to their Ga-polar counterparts, the N-polar quantum wells prepared on freestanding GaN do not exhibit any detectable photoluminescence even at 10 K. Theoretical simulations of the band profiles combined with resonant excitation of the quantum wells allow us to rule out carrier escape and subsequent surface recombination as the reason for this absence of luminescence. To explore the hypothesis of a high concentration of nonradiative defects at the interfaces between wells and barriers, we analyze the photoluminescence of Ga- and N-polar quantum wells prepared on 6H-SiC as a function of the well width. Intense luminescence is observed for both Ga- and N-polar samples. As expected, the luminescence of the Ga-polar quantum wells quenches and redshifts with increasing well width due to the quantum confined Stark effect. In contrast, both the intensity and the energy of the luminescence from the N-polar samples are essentially independent of the well width. Transmission electron microscopy reveals that the N-polar quantum wells exhibit abrupt interfaces and homogeneous composition, excluding emission from In-rich clusters as the reason for this anomalous behavior. The microscopic origin of the luminescence in the N-polar samples is elucidated using spatially resolved cathodoluminescence spectroscopy. Regardless of well width, the luminescence is found to not originate from the N-polar quantum wells but from the semipolar facets of ∨-pit defects. These results cast serious doubts on the potential of N-polar InxGa1−xN/InyGa1−yN quantum wells grown by plasma-assisted molecular beam epitaxy for the development of long-wavelength light-emitting diodes.},
  Arxiv                    = {1510.06512},
  Doi                      = {10.1103/PhysRevApplied.6.034017}
}