INVESTIGATION OF GAAS-BASED HETEROSTRUCTURE-EMITTER BIPOLAR-TRANSISTORS (HEBTS)

In this paper, we will investigate three GaAs-based heterostructure-em itter bipolar transistors (HEBTs). These HEBTs have different heterost ructure-confinement material systems, e.g., Al0.5Ga0.5As/GaAs, In0.49G a0.51P/GaAs, and Al0.45Ga0.55As/In0.2Ga0.8As/GaAs. For the studied dev ices, an n-GaAs emitter layer inserted between the confinement and bas e layer is expected to eliminate the potential spike at emitter-base ( E-B) junction. Therefore, the low collector-emitter offset voltage (De lta V-CE) is obtained. For the AlGaAs/GaAs HEBT, experimental results show that a current gain of 180 and a low offset voltage of 80 mV are acquired. In addition, for the InGaP/GaAs HEBT, the current gain is on ly 60 attributed to the use of larger emitter layer thickness (700 Ang strom) which causes a large recombination current in neutral-emitter r egime even when a large valence band discontinuity to conduction band discontinuity ratio (Delta E-v/Delta E-c) is presented. On the other h and, for the AlGaAs/InGaAs/GaAs HEBT, the Delta E-v value can be enhan ced due to the insertion of InGaAs quantum well (QW) between the n-GaA s emitter and the p(+)-GaAs base layer. Thus, the confinement effect o f minority carriers is enhanced and a current gain of 280 is obtained, simultaneously. Consequently, our studied devices will provide a good promise for the transistor design and circuit applications. (C) 1998 Elsevier Science S.A. All rights reserved.