RbF as reactive and dipole interlayers between the Ge/GaAs interface

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Abstract
We have prepared Ge/RbF/GaAs(100) and Ge/RbF/GaAs(111) heterostructures and compared their electronic and structural characteristics with the Ge/GaAs interface. The electronic properties of the heterostructures were studied using synchrotron-radiation photoemission spectroscopy and x-ray photoemission spectroscopy. The structural properties were determined by reflection high-energy electron diffraction and low-energy electron diffraction. The GaAs surfaces were initially Ga-rich in both orientations. Ge deposition on a RbF-covered GaAs(100) surface at 300 °C, followed by annealing the sandwich to 400 °C, causes a complete desorption of RbF. However, photoemission spectra of this interface showed no gallium but did show arsenic, which is quite a different result from a corresponding spectrum for Ge on clean GaAs(100). We conclude that fluorine etches gallium from the outer layer of GaAs(100). During Ge epitaxy, As atoms at the interface segregate to the surface region. Ge deposition on the RbF-covered GaAs(111) surface at 100 °C followed by annealing up to 400 °C showed, however, very little desorption of RbF. After Ge epitaxy, the core-level peaks of both Rb and F were shifted to higher binding energies. For the F 1s peak this shift was up to 1.3 eV. The Rb peak positions were shifted less than the corresponding F peaks. Shifts in the Ga 3d, As 3d, and Ge 3d peak positions could scarcely be detected. These results indicate the formation of a RbF dipole layer between the two semiconductors.