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Evidence of nanoscale Anderson localization induced by intrinsic compositional disorder in InGaN/GaN quantum wells

by Anne-Marie - published on

InGaN/GaN quantum wells (QWs), the active regions of nitride-based LEDs, display broad photo- or electro-luminescence spectra. The emission is assumed to be inhomogeneously broadened due to the contributions from material regions with different In content. Atomic Probe Tomography measurements have demonstrated that the InGaN ternary alloys indeed exhibit intrinsic compositional disorder due to the random positioning of atoms on the crystal sites. Theory predicts that this intrinsic compositional disorder should induce Anderson localization in regions of a few nm size with different eigen energies. The effects of carrier localization are suspected to strongly impact the material properties and the device performances. However, carrier localization induced by the alloy disorder have not been evidenced up to now.

We have studied the electro-luminescence of p-type single InGaN/GaN QW structures by scanning tunneling luminescence micro-spectroscopy. In this experiment, carriers are locally injected from an STM tip and the luminescence spectrum emitted from their recombination in the QW is detected as a function of the tip position. We have observed fluctuations in the electro-luminescence spectrum on the scale of a few nm, corresponding to the expected size of the localization regions induced by the intrinsic alloy disorder. Narrow emission lines, characteristic of the emission from single localized states at room temperature, are resolved. These results provide the first direct experimental evidence of Anderson localization induced by alloy disorder in InGaN/GaN heterostructures.

W. Hahn, J.-M. Lentali, P. Polovodov, N. Young, S. Nakamura, J. S. Speck, C. Weisbuch, M. Filoche, Y.-R. Wu, M. Piccardo, F. Maroun, L. Martinelli, Y. Lassailly, and J. Peretti, Physical Review B 98, 045305 (2018). DOI: 10.1103/PhysRevB.98.045305