the entire arena of low-dimensional science and technology by their own right and ?nd extensive applications in quantum registers, resonant tunneling diodes and transistors, quantum switches, quantum sensors, quantum logic gates, heterojunction ?eld-effect, quantum well and quantum wire trans- tors, high- speed digital networks, high-frequency microwave circuits, quantum cascade lasers, high-resolution terahertz spectroscopy, superlattice photo-oscillator, advanced integrated circuits, superlattice photocathodes, thermoelectric devices, superlattice coolers, thin ?lm transistors, intermediate-band solar cells, micro- tical systems, high-performanceinfrared imaging systems, bandpass ?lters, thermal sensors, optical modulators, optical switching systems, single electron/molecule electronics, nanotube based diodes, and other nanoelectronic devices.