Minority carrier diffusion lengths in MOVPE-grown n- and p-InGaN and performance of AlGaN/InGaN/GaN double heterojunction bipolar transistors

We fabricated InGaN p-n junction diode structures on SiC substrates by metalorganic vapor phase epitaxy, and investigated the minority carrier diffusion length in n- and p-InGaN layers by electron beam induced current measurements. The minority electron diffusion length in p-InGaN was little affected by the In content in InGaN. The diffusion length decreased with increasing Mg-doping concentration. The minority hole diffusion length in n-InGaN was little affected by Si-doping concentration but slightly decreased with increasing In content in InGaN. We also fabricated pnp AlGaN/InGaN/GaN double heterojunction bipolar transistors and investigated their common-emitter current-voltage characteristics. The Si-doping concentration in the base was 4×10¹⁹ cm^-3. The maximum current gain was 21 at a collector current of -10 mA for an emitter size of 30 μm×50 μm. This good performance is ascribed to the large conduction band discontinuity between the AlGaN emitter and InGaN base.