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We review a new molecular beam epitaxy (MBE) technique we call cleaved edge overgrowth (CEO), which makes possible fabrication of quantum wires or other lower dimensional quantum structures with atomic precision. CEO is accomplished by performing two separate MBE overgrowths separated by an in situ cleave of the substrate sample. We review our development of this novel method and give several examples of new structures recently fabricated using it.

We have recently demonstrated the existence of a high mobility (6.1×10 5 cm 2 /V·s) two-dimensional electron gas (2DEG) at the (110) vicinal surface formed by cleaving [L. Pfeiffer et al., Appl. Phys. Letters 56 (1990) 1697] a (100) GaAs wafer. We have now expanded this work to modulation-doped overgrowth on the cleaved edge of a multiperiod superlattice. We report here the first observation of the quantum Hall characteristics in such a two-dimensional system containing an atomically precise 71 A GaAs by 31 A Al 0.24 Ga 0.76 As compositional superlattice. The onset of Shubnikov-De Haas oscillations occurs at only 3000 G, implying the Landau cyclotron orbits are phase coherent over diameters as large as 5000 A, corresponding to more than 200 GaAs/AlGaAs interface crossings.

Thin films of YBa2Cu3O7−δ grown on 〈001〉-oriented SrTiO3 substrates attain zero resistance at a temperature of T=92 K and have a superconducting critical current, jc, of more than 3×106 Acm-2 at T=77 K. A low resistivity superconducting Cu-rich phase shows great promise for epitaxial growth on SrTiO3 substrates because of an improved lattice match in the growth direction and strong epitaxial ordering due to the presence of the new phase.