Nanoscale EELS analysis ofInGaN∕GaNheterostructures

Abstract

Kramers-Kronig transformations have been used to analyze the low-loss EELS spectrum of $\mathrm{InGaN}∕\mathrm{GaN}$ MWQs from which the ${\ensuremath{\epsilon}}_{2}(E)$ spectrum was extracted. The ${\ensuremath{\epsilon}}_{2}(E)$ spectrum contains information about absorption from the $d$ levels to the conduction bands in $\mathrm{InGaN}∕\mathrm{GaN}$ heterostructures. We have constructed maps of $\mathrm{Ga}$ distributions from the $\mathrm{Ga}$ absorption peak at $\ensuremath{\sim}23\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ instead of using the traditional edges in the energy core loss spectrum. The use of the ${\ensuremath{\epsilon}}_{2}(E)$ spectrum has shown an increased clarity in the information gained, and often the possibility of analyzing the strain within quantum wells that contain defects such as dislocations and $\mathrm{V}$-defects. It is demonstrated that the $\mathrm{Ga}$ inside the quantum wells has a nonhomogeneous distribution using this novel technique.