Ge–GaAs(110) interface formation

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Abstract
The heterojunction chemistry for Ge grown by molecular beam epitaxy (MBE) on in situ cleaved GaAs exhibits significant interdiffusion in short times at growth temperatures TG of 430°C (significantly lower critical TG than that reported for moderate‐vacuum physical vapor deposition). This results in profound changes in the electronic properties of the interface as probed by synchrotron‐radiation‐excited 3d core electron photoemission. Even when there is significant alloying of the two lattice‐matched semiconductors, there is nearly equal probability for Ge to bond to either a Ga or an As atom at the initial stage. As Ge becomes the dominant species, we find As preferentially diffusing toward the Ge side of the junction. This As is distributed throughout the overlayer in contrast to metal–semiconductor interface formation where the diffusing constituent resides only on the free, growing surface. We show that these behaviors are consistent with the kinetic and thermodynamic properties of the atomic species. The valence band discontinuity is negligible over atomic dimensions, while for an abrupt interface (TG=350°C) we measure ΔEV=0.7±0.050.3 eV. The photoemission changes character rapidly with temperature, indicating an activation barrier for the diffusion below which simple expressions for attenuation of the photoelectrons by electron–electron scattering are applicable. In that case we deduce an escape depth of 7.0±0.5 Å, indicating uniform growth of Ge, with composition changing abruptly from GaAs over ∠1 bond length in the (110) direction. A negligible (<0.2 eV) localized interface dipole layer is formed in the process.

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