Composition Analysis of III-Nitrides at the Nanometer Scale: Comparison of Energy Dispersive X-ray Spectroscopy and Atom Probe Tomography.

Bastien Bonef,Lynda Amichi,Mark Beeler,Nicolas Mollard,Miguel Lopez-Haro,Isabelle Mouton,Pierre-Henri Jouneau,Benedikt Haas,Catherine Bougerol,Eva Monroy,Adeline Grenier,Eric Robin

doi:10.1186/s11671-016-1668-2

Abstract

The enhancement of the performance of advanced nitride-based optoelectronic devices requires the fine tuning of their composition, which has to be determined with a high accuracy and at the nanometer scale. For that purpose, we have evaluated and compared energy dispersive X-ray spectroscopy (EDX) in a scanning transmission electron microscope (STEM) and atom probe tomography (APT) in terms of composition analysis of AlGaN/GaN multilayers. Both techniques give comparable results with a composition accuracy better than 0.6% even for layers as thin as 3 nm. In case of EDX, we show the relevance of correcting the X-ray absorption by simultaneous determination of the mass thickness and chemical composition at each point of the analysis. Limitations of both techniques are discussed when applied to specimens with different geometries or compositions.

Highlights

As optoelectronic devices push towards higher performance, engineering the quantum confinement at the nanoscale become the key for device design
Energy Dispersive X-ray Spectroscopy (EDX) energy dispersive X-ray spectroscopy (EDX) data have been collected on an FEI-Osiris microscope operated at 200 kV and equipped with a Brücker EDX system consisting of four silicon drift detectors which ensure a high signal-to-noise ratio even at a probe size
This study shows that the correlative use of EDX in scanning transmission electron microscope (STEM) and atom probe tomography (APT) can provide reliable composition measurements in thin nitride layers, which are structural key parameters to understand electrical and optical properties of future devices

Summary

Introduction

As optoelectronic devices push towards higher performance, engineering the quantum confinement at the nanoscale become the key for device design. For ternary or quaternary alloys, methods based on the analysis of the lattice parameters, such as X-ray diffraction, nanobeam electron diffraction [1], or geometrical phase analysis of high-resolution transmission electron microscopy images [2], cannot discriminate between strain and composition effects. Chemical analysis techniques such as energy dispersive X-ray spectroscopy (EDX) or atom probe tomography (APT) are better adapted to address this problem.

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