Elastic strain relief in nitridated Ga metal buffer layers for epitaxial GaN growth

Gallium nitride epitaxial layers were grown on sapphire by molecular-beam e pitaxy using nitridated gallium metal films as buffer layers. The mechanica l properties of the buffer layers were investigated and correlated with the ir chemical composition as determined by synchrotron radiation photoelectro n spectroscopy. Biaxial tension experiments were performed by bending the s ubstrates in a pressure cell designed for simultaneous photoluminescence me asurements. The shift of the excitonic luminescence peak was used to determ ine the stress induced in the main GaN epilayer. The fraction of stress tra nsferred from substrate to main layer was as low as 27% for samples grown o n nitridated metal buffer layers, compared to nearly 100% for samples on co nventional low-temperature GaN buffer layers. The efficiency of stress reli ef increased in proportion to the fraction of metallic Ga in the nitridated metal buffer layers. These findings suggest GaN films containing residual metallic Ga may serve as compliant buffer layers for heteroepitaxy. (C) 200 1 American Institute of Physics.