Improved Current Gain in GaN/SiC Heterojunction Bipolar Transistors by Insertion of Ultra-thin AlN Layer at Emitter-junction

GaN/SiC Heterojunction Bipolar Transistors (HBTs) with Ultra-thin AlN insertion layers at the n-GaN/p-SiC emitter junction are proposed to improve carrier injection efficiency. The current-voltage characteristics of n-GaN/AlN/p-SiC heterojunctions have exhibited very small reverse leakage and good rectification. The capacitance-voltage measurement have revealed that the conduction band offset between n-GaN and p-SiC has been reduced from -0.74 eV to -0.54 eV by insertion of AlN, indicating that the GaN/AlN/SiC heterojunction may show better electron-injection efficiency. A significantly improved common-base Current gain (alpha similar to 0.2) is obtained for GaN/AlN/SiC HBTs with initial N* pre-irradiation, while it was very low (alpha similar to 0.001) for GaN/SiC HBTs without AlN layers.