Abstract

SUMMARY: With modern techniques of crystal growth such as molecular beam epitaxy and metal-organic chemical vapor deposition it is now possible to make ultrathin semiconductor layers (or Quantum Wells; QW) the composition and doping of which are controlled down to the atomic scale. In semiconductors the characteristic lengths that determine the dynamics of elementary electronic excitations (de Broglie wavelength, Bohr radii, mean free path) range between 10 Å and 100 Å. The availability of high quality QW structures has opened new avenues for investigation of condensed matter physics under conditions of reduced dimensionality. Furthermore, by providing means to tailor locally the energy levels of semiconductors, these advances have great potential for applications in electronic and photonic technologies. By using very high purity material for the growth one obtains intrinsic-QW (i-QW) that exhibit 2D quantum size effects of the pure compounds. By the technique of modulation-doping (md) it is possible during the growth to introduce impurities selectively only in the large gap layers. In this case the impurities are spatially separated from the mobile electrons (e) or holes (h) that spill out into the QW and create very dense 2D Fermi-seas in which impurity scattering is absent.

© 1988 Optical Society of America