  Atomically-resolved mappings of the indium composition in InGaN/GaN
multi-quantum wellstructures have been obtained by quantifying the contrast in
HAADF-STEM. The quantificationprocedure presented here does not rely on
computation-intensive simulations, but rather uses EDXmeasurements to calibrate
the HAADF-STEM contrast. The histogram of indium compositionsobtained from the
mapping provides unique insights into the growth of InGaN: the transitionfrom
GaN to InGaN and vice versa occurs in discreet increments of composition; each
incrementcorresponds to one monolayer of the interface, indicating that
nucleation takes longer than thelateral growth of the step. Strain-state
analysis is also performed by applying Peak-Pair Analysisto the positions of
the atomic columns identified the quantification of the contrast. The
strainmappings yield an estimate of the composition in good agreement with the
one obtained fromquantified HAADF-STEM, albeit with a lower precision. Possible
improvements to increase theprecision of the strain mappings are discussed,
opening potential pathways for the quantification ofarbitrary quaternary alloys
at atomic scales.
