Electron spin resonance in amorphous germanium and silicon

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Abstract
The contributions to the spin resonance absorption lines observed in amorphous silicon and germanium are discussed in terms of the different relaxation processes. It is shown that besides a g-value distribution, hyperfine interaction contributes significantly. Dipolar and anisotropic exchange interactions are shown to be of minor importance except at the highest spin densities. The temperature-dependent increase in linewidth is explained by a modulation of the spin-orbit interaction owing to the motion of the carriers. A semiclassical model is used to show that the distribution of spin-flip times given by a sequence of consecutive hops in the framework of variable-range hopping can lead to the observed changes in linewidth and lineshape. Some exchange interaction is required to narrow the lines and to transfer the hopping-induced spin-flip rate to the spins far below the Fermi level. An anti-ferromagnetic exchange of the order of 1 K as reported recently, however does not seem likely in the light of the observed spin-resonance lineshapes.