A spin-polarized electron current is injected into a p-type GaAs(110) surface at 100 K using a polycrystalline ferromagnetic Ni scanning tunneling microscope tip. The injected electrons recombine to the valence band and emit circularly polarized light, and the degree of the light polarization is related to the degree of the electron polarization at the instant of recombination. Details of how to simultaneously measure the surface topography and obtain a pixel-by-pixel map of the spin-injection probability are discussed. The degree of light polarization is found to change when the electrons are injected into a clean, flat terrace versus over a step. However,the terrace-to-step polarization differences are systematically reduced as the energy of the electron is reduced. (C) 2003 American Vacuum Society.