Epitaxial growth of Fe on sulphur-passivated GaAs(100): A method for preventing As interdiffusion

We describe a new method for producing epitaxial Fe overlayers on GaAs(100), which prevents the intermixing of As in the overlayer. This is accomplished by sulphur passivation of the GaAs(100) surface in an aqueous ammonium sulphide solution, prior to Fe deposition, For growth at 25 degrees C, the initial Fe film is polycrystalline, bonding primarily to the surface Ga atoms, By an Fe coverage of 3 monolayers (ML) the epitaxial growth of well-ordered bcc Fe(100) begins. The Fe(100) surface is stabilized by some of the S which is observed to float out on top of the Fe overlayer. No evidence of As interdiffusion is observed. The S prevents As intermixing by acting as a surfactant; i.e. by holding the Fe on top of the GaAs substrate and not allowing As diffusion to occur, The resulting Fe films show a bulk-like saturation magnetization. The use of elevated temperatures (post deposition annealing and deposition at 150 degrees C) do not improve the order of the overlayer, but results in As and Ga interdiffusion.