DONOR NEUTRALIZATION BY FLUORINE-CONTAINING PLASMAS IN SI-DOPED N-TYPE GAAS CRYSTALS

CF4, SF6 and CF4/O-2 plasma-induced damage in silicon-doped n-type GaA s crystals have been investigated by using Hall measurements, X-ny Pho toelectron Spectroscopy (XPS) analysis and Secondary ion. Mass Spectro metry (SIMS) analysis. We observed that the carrier density degraded a fter plasma exposure and post annealing. The degree of deactivation of carrier density with post annealing was strongly dependent on the pla sma chemistries and the self-bias Vdc of the plasmas. From SIMS analys is, fluorine contamination was observed in the surface region of GaAs crystals after CF4 plasma exposure. The internal diffusion of fluorine atoms and the localization of fluorine atoms in n-type GaAs layers we re observed after post annealing at 400 degrees C. 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 also evaluated the effective diffusion coefficient of fluori ne in GaAs as 1.5 x 10(-11) cm(2)/s (at 400 degrees C).