Graded-emitter AlGaN/GaN heterojunction bipolartransistors

Abstract
AlGaN/GaN heterojunction bipolar transistors (HBTs) with a graded emitter-base junction have been grown and fabricated. The epitaxial structures were grown by metalorganic chemical vapor deposition on (0001) sapphire substrates. The HBT devices with an emitter size of 60 × 60 µm2 exhibit well controlled current-voltage characteristics and Gummel plots and achieve a common-emitter current gain in the range β = 4 – 10 and a common-emitter offset voltage VCEoff = 4 V at room temperature.