In this work, AIGaN/GaN high electron mobility transistors have been grown by ammonia source molecular beam epitaxy (MBE) on silicon (1 1 1), silicon carbide and GaN templates on sapphire. The structural and electrical properties of these layers have been studied in order to determine the impact of substrate choice and buffer layer on active layer quality. Furthermore, an intercalated AIN layer grown on a GaN template is shown to enhance the insulating properties of the buffer. © 2005 Elsevier B.V. All rights reserved.