Clustering equilibrium and deactivation kinetics in arsenic doped silicon

The equilibrium between clusters and dopant in solution was studied on silicon on insulator specimens uniformly doped with As at concentrations C-As from 1 to 7.6x10(20) cm(-3). The values of the carrier density n* after equilibration at 700, 800, and 900 degreesC are reported. With increasing dopant concentration n* rapidly saturates to the limiting value of the carrier density n(e), thus simulating a precipitation process. It is shown that the values of n(*) at different temperatures and dopant concentrations can be calculated by an equation derived in the Appendix by using a simple cluster model. The deactivation was analyzed by isothermal annealing of the specimens at temperatures in the range 550-800 degreesC. At high temperature the kinetics accurately complies with the rate equation -dn/dt=A{exp[-(E-alphan)/kT]-(n(0)-n)/(n(0)-n*)exp[-(E- alphan*)/kT]} which is the one reported in [D. Nobili, S. Solmi, M. Merli, and J. Shao, J. Electrochem. Soc. 146, 4246 (1999)] complemented by the second term on the right to account for the declustering process. Deviations leading to rates lower than predicted by the above equation are presented by the most heavily doped compositions after partial deactivation at temperatures less than or equal to 700 degreesC. The analysis of this phenomenon puts into evidence that clustering presents a limiting rate which only depends on temperature and carrier density, and is insensitive to As concentration.