We present a procedure whereby a sheet of donor atoms is incorporated in (100) Si during molecular beam epitaxial growth, Analysis by secondary ion mass spectroscopy and transmission electron microscopy shows that the width of such 8-function doping layers is only a few lattice planes. Tunneling spectroscopy and transport measurements give evidence for quantum confinement of the electronic charge in the layer and thus confirm the narrow width.For a number of Si device applications an extremely sharp and high density doping profile is required. In principle such a sharply defined doping layer can be achieved with molecular beam epitaxial (MBE) growth ofSi. The problem is that for Sb or Ga densities in the 10 20 em -3 range there are significant surface segregation and a low rate of incorporation into the growing Si crystal, At the typical growth temperature of -700 °C the dopants are carried along the surface of the growing crystal. The doping profile is significantly broadened. 1To overcome this difficulty two procedures have been reported in the literature. In Ref 2 the co-evaporation of a layer of Si and dopant at room temperature followed by solid phase epitaxy has been employed. Reference 3 introduces secondary ion implantation, whereby a negative potential ( -500 V) is applied to the substrate and the dopant is incorporated by knock-on from Si ions. Doping spikes of _10 19 em
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