MOLECULAR-BEAM-EPITAXY DOPING KINETICS - A RATE-EQUATION MODEL

A rate equation model based on the master equation approach is developed for the study of molecular-beam-epitaxy doping kinetics. The model includes elementary surface processes such as adsorption, evaporation, and migration of atoms. The model is applied to the study of the surface segregation phenomenon during In doping of Si. The doping studies were performed for the following growth conditions: T in the range 500-750 degrees C; a growth rate of 1 mu m/h; and a flux ratio J(In)/J(Si) equal to 2.0x10(-4). The predicted sticking coefficient of In versus 1/T shows excellent agreement with experiments. The sticking coefficient decreases with T due to surface segregation aided evaporation of In at higher temperature. The predicted dopant depth profile also shows excellent qualitative agreement with experiments. The surface segregation of In occurs due to a strong repulsive interaction between In and the host lattice. The results of this study show that there is a dopant-depleted zone (DDZ) where the In concentration is lower than both the bulk and the top surface layer The observed DDZ qualitatively matches that observed in experiments. The time and growth rate dependencies of the phenomenon are studied and found to be in good agreement with experiments. The model was used to study delta doping of dopants in the range of 673 to 973 K. The results are in qualitative agreement with experimental results. With an increase in temperature, the dopant profiles become sharper. This is caused by a smoother growing surface at higher temperatures.