Experimental quantification of atomically-resolved HAADF-STEMimages using EDX

TL;DR

This paper presents a method to quantify atomically-resolved HAADF-STEM images using EDX calibration, revealing detailed insights into InGaN/GaN quantum well growth and strain states without intensive simulations.

Contribution

The novel approach combines EDX calibration with HAADF-STEM contrast analysis for atomic-scale compositional mapping, avoiding computationally heavy simulations.

Findings

Discreet composition increments correspond to monolayer interfaces.

Nucleation duration exceeds lateral step growth.

Strain analysis aligns with composition estimates, with potential for quaternary alloys.

Abstract

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.