Graded-emitter AlGaN/GaN heterojunction bipolar transistors

AlGaN/GaN heterojunction bipolar transistors (HBTs) with a graded emitter-b ase junction have been grown and fabricated. The epitaxial structures were grown by metalorganic chemical vapor deposition on (0001) sapphire substrat es. The HBT devices with an emitter size of 60 x 60 mu m(2) exhibit well co ntrolled current-voltage characteristics and Gummel plots and achieve a com mon-emitter current gain in the range beta = 4 - 10 and a common-emitter of fset voltage V-CEoff = 4V at room temperature.