A MICROKINETIC MODEL FOR DOPING OF SILICON LAYERS DURING MOLECULAR-BEAM EPITAXY

A model is proposed for doping of silicon layers during homoepitaxy on a substrate slightly tilted from the (110) plane. The model suggests a dual mechanism of layer growth both by nucleation and trapping of si licon adatoms in geometrical growth sites (steps) on the surface, and is analysed by means of the method of correlation functions of atoms n ear the growth sites. It is shown that possible regimes of doping are governed by the competition, first, between desorption of impurity and its incorporation into the layer and, second, between ''blocking'' of the impurity adatoms near the steps and their absorption by the surfa ce vacancies. Formulae are obtained which relate the steady concentrat ion of the impurity in the layer and the width of transition concentra tion regions to the substrate temperature, growth rate, the misorienta tion angle of the substrate and the density of the impurity beam from the source. The conditions for 100% impurity transfer from the source into the layer are predicted. The obtained results are in good agreeme nt with previously published experimental data.