Epitaxial strain energy measurements of GaN on sapphire by Raman spectroscopy

Abstract

This study reports a non-destructive method of measuring the residual strain in the GaN epilayer grown on sapphire substrate by micro-Raman spectroscopy. Operating in confocal mode this method allows a depth-dependent measurement of residual strain in the epitaxial layer without prior treatment of the sample. This approach to measurement of residual strain is demonstrated on GaN epitaxial films grown by both MOCVD and H-MOVPE. In the case of MOCVD grown films, the biaxial strain energy was found to vary from 0 (GaN surface) to 5.0 kJ/mole (GaN/sapphire interface), but in the case of H-MOVPE grown samples the strain energy varied from 6.5 kJ/mole -hydrostatic strain (GaN surface) to 25.0 kJ/mole -biaxial strain (GaN/sapphire interface), indicating that the surface layer of the N-terminated H-MOVPE material is not free from strain. Estimates are given for the curvature of substrate, lattice parameter of epitaxial layer, and the interface shear modulus.

Photoluminescence and Raman studies of GaN films grown by MOCVD

“…Therefore, we move to study Raman measurement of the E 2 Raman mode that is known to be shifted by stress only [30] Raman is a powerful method to examine quality and to monitor residual stress of the GaN film. The width of the strongest mode E 2 (high) can be used to analyze lattice defects [5,31], whereas its frequency shift can be well used to monitor residual stress [5,32,33]. The residual stress due to mismatch of the lattice constants and the thermal expansion coefficients of the substrate and epitaxial film significantly effects the optical and electrical properties of epitaxial film.…”

Effect of the growth temperature on the properties of AlxGal−xN epilayers grown by HVPE

“…E 2 (high) peak positions of the Al x Ga 1 À x N epilayer were 566.25, 568.03 and 570.74 cm À 1 . The E 2 (high) peak position of GaN is 567.6 cm À 1 [13] and that of AlN is 657.4 cm À 1 [14]. The peak positions of Al x Ga 1 À x N epilayer lie between that of GaN and AlN [15].…”

Raman measurements and stress analysis in gallium ion-implanted gallium nitride epitaxial layers on sapphire

“…It has been shown in Ref. [23] that for the above defects in a GaN layer of thickness 1 µm (on sapphire substrate) the bi-axial strain energy varies from 0 (GaN surface) to 0.4 GPa (GaN/sapphire interface), indicating that the surface layer is free from this type of strain. On the other hand, the ion irradiation induces strain in the film due to point defects.…”