Common-emitter current-voltage characteristics of a Pnp AlGaN/GaN heterojunction bipolar transistor with a low-resistance base layer

We fabricated a Pnp AlGaN/GaN heterojunction bipolar transistor and investigated its common-emitter current-voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The Al mole fraction in an AlGaN emitter layer was 0.18. The thickness of the GaN base layer was 0.12 μm and its Si doping concentration was as high as 1×10¹⁹cm^-3, so its base resistance decreased two orders of magnitude compared with the reported Npn nitride heterojunction bipolar transistors. The transistor showed good saturation current-voltage characteristics and the maximum common-emitter current gain of 28 was obtained for collector current of -2×10^-5A at room temperature.