Donor neutralization by fluorine containing plasmas in Si-doped N-type GaAs crystals

摘要

CF_4, SF_6 and CF_4/O_2 plasma-induced damage in silicon-doped n-type GaAs crystals have been investigated by using Hall measurements, and SIMS analysis. We observed that the carrier density degraded with post annealing after plasma exposure. The degree of deactivation of carrier density with post annealing was strongly dependent on the plasma chemistries and the self-bias Vdc of the plasmas. From SIMS analysis, fluorine contamination was observed in the surface region of GaAs crystals after CF_4 plasma exposure. The internal diffusion of fluorine atoms and the localization of fluorine atoms in n-type GaAs layers were observed after post annealing at 400 deg. From these results, we proposed a mechanism of plasma induced damage in which internally diffused fluorine atoms neutralize the donor silicon by forming a Si-F bond. We determined the effective diffusion coefficient of fluorine in GaAs as 1.5x10~(-11) cm~2/s(at 400 deg).