(a) Micro-Raman spectra of the ALD compliant BL and MOCVD NL. The Raman peak at 578 cm−1 is ascribed to the sapphire substrate. The dashed line indicates the strain-free GaN E2 peak at 567.60 cm−1. (b–e) Two-dimensional micro-Raman mappings of the E2 peak in an area of 100 μm × 100 μm. (b) and (c) show the Raman shift relative to the strain-free GaN E2 peak (Δω) and (d) and (e) show the Raman intensity, of the ALD compliant BL and MOCVD NL, respectively.