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In this contribution, we discuss the crystalline properties of strained and strain-relaxed CVD-grown GeSn layers with Sn content in the range 6.4-12.6 at.%. A positive deviation from Vegard's law was observed and a new experimental bowing parameter was extracted for GeSn: b GeSn = 0.041 Å (in excellent agreement with recent theoretical predictions). The GeSn critical thickness for strain relaxation as a function of Sn concentration was determined, resulting in significantly higher values than those predicted by equilibrium models. A composition-dependent strain relaxation mechanism was also found, with the formation of an increasing density of GeSn pyramidal islands in addition to misfit dislocations at lower Sn concentration.

We present atom probe analysis of 40nm wide SiGe fins embedded in SiO and discuss the root cause of artefacts observed in the reconstructed data. Additionally, we propose a simple data treatment routine, relying on complementary transmission electron microscopy analysis, to improve compositional analysis of the embedded SiGe fins. Using field evaporation simulations, we show that for high oxide to fin width ratios the difference in evaporation field thresholds between SiGe and SiO results in a non-hemispherical emitter shape with a negative curvature in the direction across, but not along the fin. This peculiar emitter shape leads to severe local variations in radius and hence in magnification across the emitter apex causing ion trajectory aberrations and crossings. As shown by our experiments and simulations, this translates into unrealistic variations in the detected atom densities and faulty dimensions in the reconstructed volume, with the width of the fin being up to six-fold compressed. Rectification of the faulty dimensions and density variations in the SiGe fin was demonstrated with our dedicated data treatment routine.

The crystalline properties of strained and strain-relaxed CVDgrown GeSn layers were investigated. A positive deviation from Vegard's law was determined, resulting in the extraction of a new experimental bowing parameter for GeSn: b GeSn = 0.041 Å (in excellent agreement with recent theoretical predictions). The GeSn critical thickness for strain relaxation as a function of Sn concentration was determined, resulting in significantly higher values than those predicted by equilibrium models. A composition-dependent strain relaxation mechanism was also found, with the formation of an increasing density of GeSn pyramidal islands in addition to misfit dislocations at lower Sn concentration.

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