THE QUEST FOR THE QUANTUM DOT

Semiconductor devices that confine electrons within two-dimensional quantum wells are already in production. The zero-dimensional quantum dot promises super-efficient lasers with the ultimate in spectral purity. The theory of quantum wells, quantum wires and quantum dots is explained. Energy quantisation in quantum wells is exploited in the quantum well laser, where the quantum well is formed by a 5-10 nm layer of GaAs sandwiched between two layers of AlGaAs. The quantum wires produced at Glasgow are between 0.1 μm and 0.5 μm wide, and the depth of the etch is around 30 nm. The quantum dot would have zero degrees of freedom. Fabricating quantum dots has proved to be extremely difficult. The dots have to be very small, ideally less than 30 nm in diameter, so the demands on lithography and etching are extreme.