Compositional and optical uniformity of InGaN layers deposited on (0001)sapphire by metal-organic vapour phase epitaxy

InGaN/GaN heterostructures grown by metal-organic vapour phase epitaxy were investigated by micro-Raman spectroscopy, photoluminescence and spectrally-resolved cathodo-luminescence (CL). These methods allowed the. precise determination of the indium distribution at the microscale and macroscale. Owing to the axial symmetry of the used vertical reactor, the In molar fraction in the films normally tends to increase from the centre to the edge of the 2-inch wafers. It is also observed that for increasing In content, some additional modes appear in the Raman spectra. They are tentatively associated with In clustering phenomena, most probably occurring around bunches of threading dislocations. This hypothesis is further justified by CL spectral maps.