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17 septembre - 17:00 Soutenance de thèse de Wiebke Hahn

par Anne-Marie - publié le

Disorder-induced localization effects in nitride semiconductor compounds and devices

There are growing indications that alloy disorder controls to a large extent the electrical and optical properties of semiconductor compounds. In nitride ternary alloys, intrinsic compositional disorder, resulting from the random distribution of atoms on the crystal lattice, induces strong electronic localization effects. These disorder-induced localization effects are suspected to have a major impact on the performances of nitride-based light-emitting diodes (LEDs). It is therefore of primary importance to address this issue as huge energy savings are concerned. However, the investigation of alloy disorder effects is not trivial since the typical disorder length scale is in the nm range.

During this thesis, we developed a scanning tunneling electroluminescence (STL) spectroscopy experiment to detect the radiative recombination of electrons locally injected by a scanning tunneling microscope tip in a GaN/InGaN/GaN quantum well, similar to those present in the active region of LEDs. Narrow emission peaks are detected which are characteristic of emission from single localized states. Fluctuations in the line shape of the local electroluminescence are observed at the scale of a few nm which evidence localization effects induced by alloy disorder. These experimental results are in good agreement with the so-called localization landscape theory which provides an effective confining potential map for the carriers exhibiting nanometer size localization regions.