Influence of Substrate on Crystallographic Quality of AlGaN/GaN HEMT Structures Grown by Plasma-Assisted MBE

Results of characterization of AlGaN/GaN high electron mobility transistor (HEMT) structures grown by plasma-assisted molecular beam epitaxy (PAMBE) are reported.High resolution X-ray diraction (HRXRD) and X-ray reectivity (XRR) were applied to show that structural properties of the AlGaN/GaN layers strongly depend on the substrate used for growth.It has been found that an additional 10 µm thick HVPE GaN layer grown on a commercial GaN/sapphire substrate signicantly improves structural quality of AlGaN layer.However, the best structural parameters have been obtained for the HEMT sample grown on free-standing HVPE bulk GaN substrate.