Hybrid RBT with resonant-tunneling-diode and hetero-bipolar-transistor on InP substrate

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Abstract
We carried out sample fabrication of hybrid resonant tunneling bipolar transistors (RBT) by successive epitaxial growth of resonant tunneling diode (RTD) structures directly on the emitter of hetero bipolar transistors (HBTs). Strained layer superlattice RTD structures of In/sub 0.53/Ga/sub 0.47/As-AlAs-In/sub 0.53/Ga/sub 0.47/As-AlAs-In/sub 0.53/Ga/sub 0.47/As were used for the RTD portions. The HBT portions consisted of (In/sub 0.52/Al/sub 0.48/As)/sub 0.5/(In/sub 0.53/Ga/sub 0.47/As)/sub 0.5/-In/sub 0.53/Ga/sub 0.47/As HBT structures and their breakdown characteristics were considered. This hybrid RBT has a high concentration layer of 1 10/sup 19/ cm/sup -3/ between the emitter and the RTD which serves for the RTD lower electrode layer and the HBT emitter electrode as well. This enables the device to operate as an independent RTD or as an independent HBT, in addition to the operation as an RBT. In addition, since each of these devices can freely be designed separately without affecting each other, the degree of freedom in circuit design increases greatly. The hybrid RBTs that were trial-produced had good collector current peak-to-valley ratios of 20 at room temperatures, peak current density of 3*10/sup 4/A/cm/sup 2/, and current gain of 20. These devices also had very good breakdown and saturation characteristics that permit their use in digital circuit applications which require stable operation, reflecting the characteristics of the (In/sub 0.52/Al/sub 0.48/As)/sub 0.5/(In/sub 0.53/Ga/sub 0.47/As)/sub 0.5/-In/sub 0.53/Ga/sub 0.47/As HBT structure. These hybrid RBTs are expected to have the same speed of operation as the conventional RBTs. In addition to the above, since the speed of operation becomes faster than the conventional RBT in the independent mode of operation, these devices are extremely useful for optimal circuit design in terms of both new functions and high operation speed.