Evidence for germanium phosphide dots on Ge(001)

The Ar ion sputtered and annealed (001) surface of a 0.2 Ohm 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, approximate to 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 (similar to 10-100 kbar) compressive heteroepitaxial stress induced in the dots by the substrate. (C) 1999 American Vacuum Society. [S0734-2101(99)01403-7].