Microwave performance and structural characterization of MBE-grown AlGaN/GaN HEMTs on low dislocation density GaN substrates

We report on the structural and electrical properties of AlGaN/GaN heterostructures grown by molecular beam epitaxy on low-dislocation-density, free standing GaN substrates grown by hydride vapor phase epitaxy. Structural characterization by atomic force microscopy, transmission electron microscopy, and X-ray diffractometry reveal a smooth surface morphology, coherent interfaces, an absence of dislocations generated in the epitaxial layers, and narrow X-ray peaks. Hall measurements indicate room temperature electron mobilities of 1750 cm2/V s at sheet densities of 1.1×1013 cm−2. High electron mobility transistors exhibit excellent electrical characteristics, including output power densities of 4.8 W/mm at 10 GHz, off-state breakdown voltages of up to 200 V, and extrinsic cut-off frequencies of 36 GHz on devices with 0.45-μm gate lengths.