Concentration dependent microstructure and transport properties of the magnetic semiconductor Gd-Si

The transport properties and microstructure of amorphous Gdx Si1-x alloys are presented. The conductivity increases from x=0 through the metal-insulator transition (x=14 at. %), up to a dopant concentration of 25 at. %. A sharp cusp in the magnitude of the conductivity is then observed and the flattening of the conductivity versus temperature curve occurs at higher concentrations. These transport results are explained in terms of high-resolution electron micrographs which demonstrate the formation of nano-crystallites at x25 at. %. The flattening of the conductivity versus the temperature curve is identical to the results for annealing of a -Gdx Si1-x alloys with a low Gd concentration.