Evidence for germanium phosphide dots on Ge(001)

The Ar ion sputtered and annealed (001) surface of a 0.2 Ω cm resistivity P doped Ge crystal has been investigated in ultrahigh vacuum using scanning tunneling microscopy (STM), STM light emission, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and low energy electron diffraction. The preparation procedure results in an areal concentration of 1.0±0.5 at % of P, ≈70% of which is in compound form and the remainder in elemental form. The P atoms diffuse to the surface and subsurface regions during annealing to 880 K. The evidence is that the compound is most probably metallic GeP₃ which forms nm scale dots on the surface, while the elemental P is most probably in the subsurface region. The existence of the metallic phase is consistent with the presence of large (∼10-100 kbar) compressive heteroepitaxial stress induced in the dots by the substrate.