The electron spin resonance lineshape in hydrogenated amorphous silicon germanium alloys

The electron spin-resonance lineshape of the D-center was measured in a series of hydrogenated amorphous silicon-germanium alloys (a-Si_1-xGe_x:H). The lineshape was fitted to obtain the principal g-tensor components g| and g⊥ of a cylindrically symmetric defect; inhomogeneous strains were represented by isotropic Gaussian broadening. For elemental a-Ge:H we obtained g⊥ = 2.013 and g_| = 2.042; the result g_| > g_⊥ is not consistent with the model that the D-center in a-Ge:H is an isolated dangling bond. The lineshape in alloys was modeled by superposing the unshifted D-center lineshapes in a-Si:H and a-Ge:H with an additional cylindrical symmetry line with arbitrary g-tensor and broadening. The parameters of this new line were fairly constant for x > 0.20. Models for these results based on delocalization onto two dangling bonds are discussed.