Wurtzite Al_xGa_1-xN bulk crystals grown by molecular beam epitaxy

We have studied the growth of wurtzite GaN and Al_xGa_1-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 Al_xGa_1-xN layers up to 10 [mu]m in thickness. Undoped wurtzite Al_xGa_1-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 Al_xGa_1-xN wafers can be grown is very significant for the potential future production of wurtzite Al_xGa_1-xN substrates optimized for AlGaN-based device structures.