The remarkable progress in semiconductor technology has allowed us to form various ultrathin layered structures with feature sizes of 10-30 nm. In such systems, electrons are quantum mechanically confined to form a series of standing wave states fi(z) with discrete energies Ez(i), while their in-plane motion remains free. Indeed, such a two dimensional (2-D) electron gas plays now very important roles both in solid-state physics and electronics.
Although the 2-D electron system is still a fertile field, there are vast fields of nanostructures, where new classes of phenomena are being disclosed and exploited. In this lecture, we review and discuss such studies.
First we describe various attempts, by which the tunnel escape process of electrons through the barrier layer is quantum mechanically controlled; we examine how they can be used in realizing such devices as intersubband infrared detectors, ultrafast resonant tunnelling diodes, and quantum-beat oscillators.
Second, we review a series of work to confine electrons in quantum-wire and/or quantum dot strucutres and discuss what kind of unique properties or functions have been and will be found in such 1-D and 0-D systems. We examin the current status of nanotechnology by which 10-nm scale wires and dots are formed.