I N D U S T R I A L R E S E A R C H

1 6 4 H I G H L I G H T S 2 0 2 3 I

PRINCIPAL PUBLICATION AND AUTHORS

Nanoscale mapping of the full strain tensor, rotation, and composition in partially relaxed InxGa1N layers by scanning diffraction microscopy, C. Richter (a,b), V.M. Kaganer (c), A. Even (d), A. Dussaigne (d), P. Ferret (d), F. Barbier (d), Y.-M. Le Vaillant (e), T.U. Schülli (b), Phys. Rev. Appl. 18, 064015 (2022); https:/doi.org/10.1103/PhysRevApplied.18.064015 (a) Leibniz-Institut für Kristallzüchtung (IKZ), Berlin (Germany) (b) ESRF (c) Paul-Drude-Institut für Festkörperelektronik (PDI), Berlin (Germany) (d) University of Grenoble-Alpes, CEA, LETI, Minatec Campus, Grenoble (France) (e) Nelumbo Digital SAS, Crolles (France)

REFERENCES

[1] A. Even et al., Appl. Phys. Lett. 110(26), 262103 (2017).

Nanoscale mapping of strain and composition in thin films for semiconductor devices

Scanning X-ray diffraction microscopy (SXDM) was used to quantitatively map strain within transferred (In,Ga)N layers with sub-micron resolution. The data revealed anisotropic strain relaxation effects resulting from processes involved in the production of pseudo-substrates.

Epitaxial thin films are the basis for most modern semiconductor (opto)electronic devices, such as light- emitting diodes (LEDs), transistors and integrated circuits. The electronic and optical properties of such crystalline materials can be optimised by lattice strain engineering, but non-destructive, accurate measurements of strain are not routinely available.

In this work, the SXDM technique at the strain microscope beamline ID01 was used to map strain throughout both layers of an epitaxial InxGa1-xN / InyGa1-yN double layer. The bottom layer was lifted off the original GaN substrate, transferred, patterned and annealed to mediate strain relaxation, which is desired to facilitate higher indium content in subsequent growth of the second InxGa1-xN layer (x ≈ 5%) and thus to shift its optical emission towards the red (Figure 132a) [1]. The target was to quantify the relaxation in both layers and its effect on indium content, which can be inferred from the unit-cell dimensions.

The results in Figure 132b show that the relaxation is most efficient at the mesa edges. Interestingly, these regions do not show the highest incorporation of indium into the regrown top-layer, which was attributed to an increased number of dislocations and V-shaped pits during the regrowth. This work paves the way for routine application of SXDM to study strain distribution in epitaxial layers, microstructures and devices.

Fig. 132: a) A sketch of the structured sample after transfer and subsequent regrowth. b) Maps of strain components for the regrown layer and maps of composition for both layers. Scale bars correspond to 5 µm.