Impurity distribution in epitaxial films condensed from vapour or molecular ion beams

Abstract

A comparative treatment of the principal methods of describing the processes of doping of epitaxial semiconductor films was made: a thermodynamic treatment with the use of kinetic concepts on the reactions and transport phenomena in a gaseous phase; a statistic-probability one using energy characteristics of interaction of dopant atoms or ions with the main substances and with the substrate; computer simulation by the methods of random numbers. The concentration of a captured impurity in the film decreases or increases depending on the mechanism limiting dopant transport: viz., with mass transport prevailing in a gaseous phase n“[tilde]” V -1, or with diffusion on the surface n“[tilde]” V -0.5. If the doping is limited by the building-in of atoms, t he distribution coefficient can decrease (or increase) towards unity with rate. Oscillations in the distribution of an impurity in the film at the initial stage of epitaxy from molecular ion beams are observed. The simulation method permits one to find out doping inhomogeneity over the film bulk due to the difference in interaction energies for atoms of the impurity and of the main substance.