RF-MBE grown AlGaN/GaN HEMT structure with high Al content

A Si doped AlGaN/GaN HEMT structure with high Al content (x=43%) in the barrier layer is grown on sapphire substrate by RF-MBE. The structural and electrical properties of the heterostructure are investigated by the triple axis X-ray diffraction and Van der Pauw-Hall measurement, respectively. The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface. The high 2DEG mobility in excess of 1260 cm2/(V&middots) is achieved with an electron density of 1.429 × 1013 cm-2 at 297 K, corresponding to a sheet-density-mobility product of 1.8 × 1016 V-1 &middot s-1. Devices based on the structure are fabricated and characterized. Better DC characteristics, maximum drain current of 1.0 A/mm and extrinsic transconductance of 218 mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer. The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.