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Raman spectroscopic characterization of epitaxially grown GaN on sapphire

 

Raman spectroscopy was applied to investigate the residual thermal strain in thick GaN layers grown epitaxially on sapphire substrates by hydride vapour phase epitaxy. The thickness of the GaN layers varied from 20 to 300 µm. The strain distribution in the GaN layers as a function of the distance from the GaN/sapphire interface was determined non-destructively applying the confocal technique. The layers were found to be exposed to compressive stress whereas a stress relaxation from the GaN/sapphire interface to the top of each GaN film could be observed.

The redshift of the E2(high) phonon mode from the bottom to the top of the GaN layer was correlated with the curvature of the samples. Using a mechanical wafer bending model as well as finite element method calculations the simulated peak position of the E2(high) phonon as a function of the GaN layer thickness agreed well with the observed wavenumber of the E2(high) mode.

 

source: iopscience

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