- 1 - 8 . 4 Quantum Well Tunneling Devices

A INTRODUCTION Advances in epitaxy have permitted the design of semiconductor devices with sufficient precision to make use of quantum mechanical tunneling. The potential advantages of tunneling-based devices consist of high-speed operation and higher functionality inherent in their strongly nonlinear current-voltage characteristics, while the disadvantages include the relative weakness of quantum effects at room temperature and the difficult integration into mainstream semiconductor technology. To date, these difficulties have largely impeded tunneling devices from evolving beyond the research stage, but continuing progress in epitaxy, fabrication and novel device concepts may render these devices suitable for some applications. Section B of this Datareview will cover the extensively researched double-barrier resonant tunneling structure (RTS) as a discrete device, as well as a two-terminal nonlinear component in simple circuits, and discuss the prospects of three-terminal operation. Optical sources and detectors based on intersubband transitions in quantum wells populated or emptied by tunneling are discussed in Section C. Tunneling devices sufficiently small to employ single-carrier or Coulomb blockade effects that offer distant prospects of general-purpose single-electron logic or more immediate possibilities of high-precision current sources are discussed in Section D. Finally, expanding the definition of a device to include tunneling structures that provide experimental probes of the electronic and structural properties of quantum wells, we discuss double-barrier and double-well RTS as spectroscopic systems for subband dispersions, carrier coherence lifetimes, and strain distributions.