Spin Polarized STM Studies of Fe Dopants and Dimers on the GaAs (110) Surface

The characterization and control of single impurity states in semiconductors is of fundamental interest, and underlies a variety of approaches for next-generation classical and quantum computing. Here we report a joint experimental / theoretical study of individual Fe atoms, substituted for Ga in the GaAs(110) surface. Spin-resolved scanning tunneling microscopy reveals a variety of charge / spin states of the Fe dopants through distinct contrast in topographic imaging and distinct electronic states in tunneling spectroscopy. To study magnetic interactions, dimers of Fe are formed by STM atomic manipulation with controlled separation, and also exhibit distinct contrast and electronic states. The experimental results are consistent with our density functional theory calculations, which show a variety of spin-polarized states in the energy range studied. Comparison with bulk- and surface-slab calculations provides insight into how the surface influences the properties of individual and coupled Fe dopants.