GAAs High-Speed Devices: Physics, Technology, and Circuit Applications

11

RESONANT-TUNNELING TRANSISTORS

11.1 INTRODUCTION TO RESONANT-TUNNELING TRANSISTORS

The first paper on tunneling devices discussed the tunnel diode was written by L. Esaki in 1958 [Esa58]. In 1965 a remarkable, pioneering paper [Mor65] titled “From Physics to Function” introduced the concept of functional device [Cap90]. The key characteristic of such devices is that “they promise to reduce greatly the number of elements and process steps per function when their capabilities are properly matched to an old or new system function.” Morton provided a few examples of functional devices, one of which was the tunnel diode.

The strength of Morton's vision was that he foresaw dramatic progress in growth techniques, equipment development, and semiconductor physics [Cap90]. The advent of advanced epitaxial growth techniques, such as MBE and MOCVD as discussed in Chapter 3, and of band-gap engineering [Cap87] has made possible the development of a new class of materials and heterojunction devices with unique optical and electronic properties. Heterojunction superlattices and their transport properties were first investigated by Esaki and Tsu in 1970 [Esa70]. They predicted negative conductance associated with electron transfer into the negative mass regions of the minizone and Bloch oscillations. Pioneering work on resonant tunneling through a heterostructure quantum well was done by Tsu, Esaki, and Chang [Cha74]. The study of the negative differential resistance (NDR) of the resonant-tunneling ...