(V)EELS characterization of InAlN/GaN distributed Bragg reflectors

Abstract

Ten-period InAlN/GaN distributed Bragg reflectors are examined by aberration corrected scanning transmission electron microscopy and by valence electron energy-loss spectroscopy (VEELS) with sub-nanometric spatial resolution and sub-eV energy dispersion. Deconvolution and peak subtraction methods, implemented in Matlab routines, are applied to the low loss region of the obtained VEEL spectra to retrieve information about the band gap energy and chemical composition, whereas a Kramers-Kronig transformation is used to retrieve the complex dielectric function of the examined material. The VEEL measurements reveal significant compositional variations in InAlN layers and show a ∼2nm thick InAlN layer with high indium content at each GaN/InAlN interface.