Design and characterization of GaAs-Ga/sub 0.89/In/sub 0.11/N/sub 0.02/As/sub 0.98/-GaAs NpN double heterojunction bipolar transistors with low turn-on voltage

GaAs-based heterojunction bipolar transistors (HBTs) have achieved widespread in high performance microwave and digital applications. However, they have a large base-emitter turn-on voltage V/sub BE/ of 1.4 V (at high current density). It is important to develop techniques to reduce V/sub BE/, particularly for low power applications. In this work, NpN double heterojunction bipolar transistors (DHBTs) were fabricated on a GaAs substrate with a Ga/sub 0.89/In/sub 0.11/N/sub 0.02/As/sub 0.98/ base that has a bandgap energy of 0.98 eV. These devices have a turn-on voltage V/sub BE/ that is 0.4 V lower than that of their GaAs base counterparts, allowing operation with lower power supply voltage and reduced power dissipation. To overcome the large conduction band discontinuity between GaAs and Ga/sub 0.89/In/sub 0.11/N/sub 0.02/As/sub 0.98/, both chirped compositional grading and delta doping were employed. In this paper, we report our first Ga(0.89)In/sub 0.11/N/sub 0.02/As/sub 0.98/-base DHBT results, which has a substantially greater V/sub BE/ reduction. The samples were grown by GSMBE with thermally cracked arsine and RF-plasma nitrogen radical beam as the arsenic and nitrogen source, respectively.