Near Field Optical Imaging of Carrier Localization in AlxGa1-xN Alloys

The wide band gap semiconductor alloys have attracted considerable attention for efficient UV emitters and laser applications. In the presence of high dislocation densities associated with growth on lattice mismatched substrates, it has been shown that carrier localization created by nanoscale compositional inhomogeneities can lead to enhanced emission efficiencies, we have investigated the origin of the localization effect using near-field optical spectroscopy using fiber coupled UV laser. We compare the spectral and spatial properties of the localization features under excitation at 244nm (above bandgap of the matrix) and 325nm (below bandgap of the matrix). Even under the latter excitation, the localized emission peak appears, suggesting a direct excitation of the localization regions.