Electron-spin-resonance study of boron-doped amorphousSixGe1−x: H alloys

Abstract

We report on ESR and Raman spectroscopy in $a\ensuremath{-}{\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$: H prepared by glow discharge with a 1-vol% boron-doping level. For most silicon contents $x$, a preferential deposition of germanium into the solid film is found. The Raman spectra show that the samples are amorphous and that no phase separation is present. Four different ESR resonances can be observed over the compositional range investigated ($0<x<0.7$) at 20 K: the known resonances of the Ge dangling bonds and of localized holes in Ge---Ge bonding states, a signal due to carbon impurities, and a new resonance with strong negative $g$-value shift ($g=1.925$) that seems to be related to surface states. A model for the density of states in the amorphous Si-Ge alloys is proposed that can qualitatively account for the experimental results.