AlN/AlGaN/GaN/AlGaN multilayer heterostructures with quantum well channel on heat conducting substrates for power microwave transistors

Molecular beam epitaxy using ammonia as a nitrogen source is applied to obtain III-nitride multilayer heterostructures having high structural quality and low dislocation density. To provide strong carrier confinement in two-dimensional electron gas for collapse-free transistor operation, GaN quantum well as thin as 5 nm was formed between AlGaN barrier layers of various Al content, keeping high sheet conductivity in 280-350 Ohm/square range. Due to rather thick AlN "template" grown at extremely high (up to 1200 degrees C) substrate temperatures directly in the same growth run prior to the growth of heterostructure, technology developed on sapphire is easily transferred to alternative substrates, for example AlN/SiC or Si. In contrast to sapphire, where noticeable drop of transistor saturation current at drain voltages higher than 5-10 V is usually observed, heat conducting substrates allow to avoid this negative thermal effect and no drop is observed at drain voltages up to 20 V and even higher. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim