Epitaxy, overlayer growth, and surface segregation for Co/GaAs(110) and Co/GaAs(100)-c(82)

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Abstract
We present high-resolution synchrotron-radiation core-level photoemission results which show that the room-temperature deposition of Co onto GaAs(110) induces limited substrate disruption, leading to Ga and As intermixing with the metal overlayer. High-energy Auger electron diffraction and low-energy electron diffraction measurements indicate that Co orders weakly to form a metastable, epitaxial bcc matrix with principal crystallographic axes parallel to those of the substrate. Angle-dependent x-ray photoemission results show that the distribution of Ga and As in the Co overlayer varies with, and is dependent on, the Co thickness. Together, these results show that the amount of dissociated Ga and As in the overlayer decays exponentially away from the Co/GaAs interface (1/e length 3 Å); that As surface segregates and its concentration profile is exponential away from the vacuum into the Co overlayer (surface concentration 5.8 at. % at 150-Å Co thickness, 1/e decay length 5 Å); and that the As solubility in the Co film far from either boundary is 0.26 at. %. This paper demonstrates that substrate disruption and epitaxial growth are not mutually exclusive provided that the disruption is not too severe and that conditions necessary for epitaxy exist.