Solid state interdiffusions in epitaxial Fe/GaAs(001) heterostructures during ultrahigh vacuum annealings up to 450 °C

We have used a set of complementary experimental techniques to characterize an epitaxial structure (25 nm Fe)/GaAs(001) annealed at 450 °C under ultrahigh vacuum conditions. The solid state interdiffusion leads to the formation of an epitaxial reaction layer made of ${\mathrm{Fe}}_{\mathrm{2}}\mathrm{As}$ patches embedded in a Ga rich ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{Ga}}_{\text{2−X}}{\mathrm{As}}_X$ ternary phase. The epitaxial character of this layer explains how the usually reported epitaxial growth of Fe on GaAs performed in the temperature range of 175 to 225 °C is possible in spite of the species intermixing occurring at the interface. Moreover, the observed grains of ${\mathrm{Fe}}_{\mathrm{2}}\mathrm{As}$ explain the decrease of magnetization at the interface in such contact, since ${\mathrm{Fe}}_{\mathrm{2}}\mathrm{As}$ is an antiferromagnetic alloy.