Cs incorporation in semiconductors during low-energy bombardment: A dynamic computer simulation study

Abstract

The implantation and retention of Cs atoms during low-energy irradiation of different materials (Si, Ge, and InP) was investigated by dynamic computer simulations using the Monte-Carlo code T-DYN that takes into account the gradual change of the target composition due to the Cs irradiation. The Cs incorporation was studied for four impact energies (0.2, 0.5, 1, and 3 keV) and for incidence angles ranging from 0° to 85°. For selected irradiation conditions, different values of the Cs surface binding energy U Cs (0.4, 0.8, and 2.4 eV) were used. The total implantation fluences were chosen to lie well above the values required to reach a stationary state. The steady-state Cs surface concentration, c Cs, exhibits a distinct dependence on impact energy and angle, and on U Cs; it decreases with increasing incidence energy and angle. Furthermore, increasing U Cs results in a pronounced increase of c Cs. The computed values of c Cs appear to be higher than corresponding data from experiment. Under equilibrium, the partial sputtering yields of the target, Y X, depend only weakly on U Cs, but vary with the Cs energy and angle. Y X exhibits the usual dependence on incidence angle, first increasing up to a maximum value (at ∼65°–75°) and declining sharply for larger angles. For all bombardment conditions a clear preferential sputtering of Cs atoms as compared to the target atoms is found; typically, preferential sputtering of Cs increases with decreasing irradiation energy and incidence angle, and with decreasing U Cs.