Characterization of Complex Stacking of Semiconductors Through Near Field Imaging and Spectroscopy

While high operating temperature infrared photodetection remains a major technological objective, huge improvements have been obtained through the use of increasingly complex semiconductors epitaxies such as quantum cascade structures or III-V superlattice junction. However, the characterization of these layers is challenging and often requires the use of destructive processes. Here, SNOM imaging and spectroscopy on a mechanically cleaved facet is used to characterize the different layers of a complex epitaxial heterostructure composed of a type II superlattice and highly doped semiconductors. These near-field experimental data are compared to simulation in order to retrieve both the cut-off frequency of the superlattice and the doping level of each highly doped semiconductor layers. Additionally, information about interfaces is optically retrieved through hyperspectral characterization of plasmons propagating at these vertical interfaces. In parallel, all the materials and exact stacking of the epitaxy are confirmed through scanning transmission electron microscopy.