High current gain graded GaN/InGaN heterojunction bipolar transistors grown on sapphire and SiC substrates by metalorganic chemical vapor deposition

High-current-gain GaN/InGaN double heterojunction bipolar transistors having a graded-base and emitter design grown on sapphire and SiC substrates by metalorganic chemical vapor deposition are presented. Improved device performances result from the improvement of the InGaN graded layer material quality and the p-type doping enhancement as well as the improvement of device fabrication techniques. The devices show common-emitter incremental current gain values above 35. Device operation is demonstrated at temperatures as high as 300 degrees C. The results demonstrate the potential of the graded InGaN emitter-base junction design for high-performance III-nitride heterojunction bipolar transistors. (c) 2006 Elsevier B.V. All rights reserved.