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Towards rapid nanoscale measurement of strain in III-nitride heterostructures
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View: Figures


Image of FIG. 1.
FIG. 1.

HAADF STEM image of a typical nanoribbon structure investigated in this work with a magnified view of the HEMT layers shown in the top inset. Bottom inset illustrates several HEMT nanoribbons in cross-section with metal contact and covered in passivating AlO. Indicated composition of the layers is based on the nominal growth values.

Image of FIG. 2.
FIG. 2.

A 5.5 nm probe shown in (a) was used to produce NBED patterns along the [110] zone axis, such as the reference pattern seen in (b). The growth-direction strain profile obtained from NBED for the nanoribbon HEMT structure seen in (c) is presented in (d).

Image of FIG. 3.
FIG. 3.

(a) HAADF STEM image of HEMT structure used to create GPA strain maps. The -vectors (0002) and (011) are first selected from a FFT image (b). Raw phase and amplitude images are calculated from each vector and shown in (c)–(f). Strain maps are calculated for both the growth direction (g) [0002] and the in-plane direction (h) [010] with the scale shown to the far right.

Image of FIG. 4.
FIG. 4.

Growth-direction strain maps with spatial resolutions of (a) 5 nm and (b) 2 nm generated from the HAADF STEM image shown in Figure 2(a) with the strain scale indicated at the bottom. (c) Linescans are obtained from each image as indicated in (a) and integrated over the whole field of view.

Image of FIG. 5.
FIG. 5.

A summary of strain profiles generated using GPA, NBED, and FEA simulations. The inset shows a scaled cross section of the HEMT structure. Comparing the two experimentally obtained strain profiles highlights the advantages of each technique used, namely: better spatial resolution of GPA and lower noise of NBED. Two curves obtained from FEA simulations demonstrate how the modified structure based on experimental measurements of the layers' compositions improve the fit of the strain profile with experimental data over that profile obtained from the nominal structure.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Towards rapid nanoscale measurement of strain in III-nitride heterostructures