Growth and microstructure dependence of electronic and magnetic properties in magnetically doped Gd-Si amorphous semiconductors

Abstract

A comparision of the electronic and magnetic properties of amorphous ${\mathrm{Gd}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ $(a\text{\ensuremath{-}}\mathrm{Gd}\text{\ensuremath{-}}\mathrm{Si})$ thin-film alloys prepared by different growth techniques ($e$-beam evaporation and magnetron sputtering) is reported. High-resolution cross-sectional transmission electron microscopy (HR-XTEM) and Rutherford backscattering (RBS) show that the material microstructure is highly dependent on deposition method and growth conditions. Electron-beam-evaporated films have columnar microstructure (column width $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$) while magnetron-sputtered films prepared at low argon partial pressure are featureless. However, the dc conductivity, magnetoresistance, and $M(H,T)$ properties of the films are totally independent of this difference in microstructure at the length scale of $10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. RBS shows that the films have the same overall atomic number density, independent of Gd incorporation, for a wide range of doping concentrations (up to $18\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$), and HR-XTEM shows a dense, homogenous, and amorphous phase with no clustering at the atomic level. The independence of properties from the nanoscale microstructure strongly argues that the magnetic moment and charge carrier behavior observed previously are a result of fundamental interactions at the atomic level. Films sputtered at high argon pressure are less dense and have an open columnar microstructure which leads to fast degradation of film properties due to massive bulk oxidation.