Multiple InGaN QW heterostructure

Abstract This chapter presents a detailed examination of an In x Ga 1 − x N multilayer structure, composed of alternating In-rich quantum wells (QWs) and In-deficient barriers. The nominal widths of these semiconductor layers are 1.5 nm and 6 nm, for the QW and barrier layers, respectively. This is, thus, a structure with features in the nanometer size range, smaller than the two structures examined in the preceding chapter. Again, our STEM examination consists in the simultaneous acquisition of HAADF images and spatially resolved low-loss EELS-SI, that are used in combination. However, this time, we also present a detailed analysis of high resolution HAADF images, that provides additional evidence of chemical and structural changes in the layers. Subtle changes in the valence properties of the materials, band gap energy, plasmon excitation, and also elemental transitions are monitored by low-loss EELS. Kramers–Kronig analysis (KKA) of the energy-loss spectrum is used to extend the dielectric characterization. In this sense, we apply a method for the experimental characterization of the plasmon excitation in the CDF based on our findings in Chapter 3, consisting in the determination of E c u t in the CDF. Apart from this, we compute spatially localized electron effective mass values from our CDFs, as we expect some contrast in the QW region. Finally, we examine the intensity of the Ga 3d transition in a previously normalized SSD. We show how this can be carried out after KKA, revealing the gallium concentration distribution with an excellent spatial resolution.