Heterostructure confinement effect on the negative-differential-resistance (NDR) bipolar transistor

We review the current investigation of heterostructure-emitter bipolar transistors (HEBT) and pay attention to confinement effects on the common-emitter current gain and the occurrence of negative-differential resistance (NDR). Three main devices with different heterostructure emitters have been grown and discussed. These devices include single-(SHEBT), double-(DHEBT), and resonant tunneling-(RT-HEBT) structure with Al 0.5 Ga 0.5 As/500A-GaAs, Al 0.5 Ga 0.5 As/500A-GaAs and 5-period 50A-Al 0.5 Ga 0.5 As/50A-GaAs superlattic emitters, respectively. With respect to current gain, it is found that Al 0.5 Ga 0.5 As/500A-GaAs gives the best confinement effect on hole minority carriers We obtain common-emitter current gains of 180, 18, and 65 for the SHEBT, DHEBT and RT-HEBT, respectively. Besides, all of the studied devices exhibit an interesting S-shaped negative-differential resistance (NDR) resulting from the regenerative switching process. With respect to NDR performance, the Al 0.5 Ga 0.5 As/500A-GaAs, shows the best confinement effect on the ionized electrons. The controlled voltage efficiencies are 1.43, 1.77, and 1.12 for SHEBT, DHEBT, and RT-HEBT, respectively.