Recent quantum effect nanometer-scale devices can be divided into three categories. 1) Quantum wave devices, which use the electron-wave transport and control the phase of the electron wave. 2) Quantum functional devices, which use quantum effects, such as size and tunneling effects in ultrafine structures. 3) Atomic or molecular devices, which use the motion of the atom or molecule. Single electron devices could be included in the quantum functional device category. This paper reviews our research activities on quantum functional devices and discusses our future research direction. Using multi-emitter RHETs, logic and memory circuits could be constructed with fewer transistors and resistors. Our research on this quantum functional device will be going in two different direction. One is to scale it down further to make quantum-dot-tunneling transistors, QHETs. New process technology is described to make these quantum dot tunneling structures using a GaAs (111)B substrate, and 10 nm wiring embedded in device structures. The other direction is to develop more practical quantum functional devices. One example is the development of a multi-emitter bipolar transistor which has highly doped emitter and base regions to allow interband tunneling. This device operates at room temperature and could be potentially used in bipolar circuits. Also this device has a potential to be used as a new functional phototransistor.
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