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Molecular beam epitaxy of free-standing wurtzite AlxGa1xN layers

Novikov, Sergei V. and Staddon, C.R. and Martin, Robert and Kent, A.J. and Foxon, C. Thomas (2015) Molecular beam epitaxy of free-standing wurtzite AlxGa1xN layers. Journal of Crystal Growth, 425. p. 125. ISSN 0022-0248

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Recent developments with group III nitrides present AlxGa1xN based LEDs as realistic devices for new alternative deep ultra-violet light sources. Because there is a significant difference in the lattice parameters of GaN and AlN, AlxGa1xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE). Thick wurtzite AlxGa1xN films were grown by PA-MBE on 2-in. GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1xN samples. X-ray microanalysis measurements confirm that the AlN fraction is uniform across the wafer and mass spectroscopy measurements show that the composition is also uniform in depth. We have demonstrated that free-standing wurtzite AlxGa1xN wafers can be achieved by PA-MBE for a wide range of AlN fractions. In order to develop a commercially viable process for the growth of wurtzite AlxGa1xN substrates, we have used a novel Riber plasma source and have demonstrated growth rates of GaN up to 1.8 mm/h on 2-in. diameter GaAs and sapphire wafers