Characteristics of functional heterostructure-emitter bipolar transistors (HEBTs)

We have fabricated and discussed the performances of the InGaP/GaAs and AlGaAs/GaAs HEBTs. From the calculation, an emitter thickness not smaller than 230 and 320 Å is needed to eliminate the emitter-base (E-B) potential spike for an InGaP/GaAs and an AlGaAs/GaAs HEBTs, respectively. For the studied InGaP/GaAs HEBT, a wide emitter thickness of 700 Å degrades the d.c. performance due to the bulk recombination effect in the emitter neutral region under the large E-B forward bias. In addition, we observe a multiple S-shaped NDR resulting from an avalanche multiplication and successive barrier lowering process as operated in the inverted mode. Whereas the AlGaAs/GaAs HEBT with an emitter thickness of 500 Å is properly designed to obtain a high current gain and a low offset voltage. However, we observe only a single S-shaped NDR for the AlGaAs/GaAs HEBT. This is due to the barrier lowering effect attributed to the fact that the hole's and electron's accumulation occur simultaneously. Both the transistor action in normal operation mode and the presence of NDR make our studied devices very promising for the analog and logic circuit applications.