HALOGENATION OF GAAS (100) AND (111) SURFACES USING ATOMIC-BEAMS

GaAs (100) and (111) gallium-rich surfaces (Ga/As congruent-to 1.4) have been halogenated using beams of atomic chlorine and fluorine under ultrahigh-vacuum conditions. XPS and LEED analyses of the resulting thin films indicate that chlorine atoms produce a disordered highly arsenic-deficient GaCl(x) reaction product layer whose thickness decreases as temperature increases from 130 to 273 K. At 323 K and above, a stable reaction layer is not observed but an ordered, stoichiometric to As-rich GaAs surface is formed; a residual submonolayer of chlorine is present at temperatures up to 573 K. More limited studies on arsenic-rich GaAs surfaces (Ga/As congruent-to 0.85) indicate identical behavior at temperatures of 173 K and above. At 140 K, though, preferential etching does not occur and equal amounts of AsCl(x) and GaCl(x) are observed. Fluorination of Ga-rich GaAs (100) surfaces at 305 K produces a disordered GaF3 layer which is thermally stable (no loss of fluorine) up to a temperature of 573 K. These results indicate that any realistic model of chemical etching of GaAs should admit the possibility (if not likelihood) of the formation of a three-dimensional reaction product layer, whose thickness and chemical composition are a function of halogen atom flux and substrate temperature.