Pressure-dependent photoluminescence study of epitaxial AlGaN to 19 GPa

We report a high-pressure study of the room temperature photoluminescence from an Al_0.1Ga_0.9N epilayer and GaN buffer grown by low-pressure metalorganic vapour phase epitaxy on sapphire. An excimer laser based lift-off technique was used for the processing of the epilayer, which enables the loading of strain-relaxed samples of epitaxial nitride materials into a diamond anvil cell apparatus. In this way the band gap pressure dependences of an Al_0.1Ga_0.9N epilayer and its GaN buffer layer were measured up to a pressure of 19 GPa. The measured band gaps were found to follow the expected theoretical dependences with some modification of the deformation potentials determined by previous lower pressure studies. Above 19 GPa, no photoluminescence was observed, possibly due to a structural phase transition in the Al_0.1Ga_0.9N epilayer.