Npn-type AlGaN/InGaN/GaN heterojunction bipolar transistors have been fabricated for high power application. Their common-emitter current-voltage characteristics showed a high breakdown voltage of 120 (V), corresponding to the breakdown electric field of 2.3 (MV/cm) in the collector. This value is comparable to the expected one for the wide bandgap of GaN (3.3 (MV/cm)). The cross-section transmission electron microscopy image showed that the V-shape defects in InGaN were filled with wider bandgap AlGaN layers during the emitter growth. This is considered to prevent the leakage current from the base to the collector, resulting the high breakdown electric field.
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