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PACS 78.55.Cr, 81.15.Gh Gallium nitride layers were grown epitaxially on sapphire substrates in a LP-MOCVD reactor using trimethylgallium and ammonia. GaN films were also obtained by nitridation, exposing GaAs substrates to ammonia in the same reactor under similar conditions. The temperature ranged between 750 °C and 900 °C, while the pressure was adjusted between 75 and 585 Torr. Photoluminescence measurements were made on the samples using a 325 nm He -Cd laser; near band edge emission and subbandgap luminescence were observed. The luminescence color of the sapphire grown layers went from orange to yellow-green, while it ranged from yellow to blue-violet in the nitridated samples.

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