We have studied the growth of wurtzite GaN and AlxGa1-xN layers and bulk crystals by molecular beam epitaxy (MBE). MBE is normally regarded as an epitaxial technique for the growth of very thin layers with monolayer control of their thickness. However, we have used the MBE technique for bulk crystal growth and have produced 2 in diameter wurtzite AlxGa1-xN layers up to 10 mu m in thickness. Undoped wurtzite AlxGa1-xN films were grown on GaAs (1 1 1)B substrates by a plasma-assisted molecular beam epitaxy (PA-MBE) method and were removed from the GaAs substrate after the growth. The fact that free-standing ternary AlxGa1-xN wafers can be grown is very significant for the potential future production of wurtzite AlxGa1-xN substrates optimized for AlGaN-based device structures. (C) 2011 Elsevier B.V. All rights reserved.