Electron spin resonance in lasercrystallized polycrystalline silicon-germanium thin films

The defect properties of laser-crystallized polycrystalline silicon-germanium (Si-Ge) thin films on glass substrates were investigated with electron spin resonance (ESR) and conductivity measurements. The ESR measurements reveal that lasercrystallized poly Si _1-xGe _x thin films with 0<x<0.84 contain a dangling-bond concentration of about N _s=4×10 ₁₈ cm ^-3, roughly independent of the Ge content in this range. Surprisingly, the ESR signal vanishes completely for the Ge-rich alloys (x>0.84) and instead a broad atypical signal appears that we attribute to electric dipole induced spin resonance (EDSR). Samples that showed this behavior exhibited a nearly temperature- independent electrical conductivity for temperatures between 20 and 100 K. The data are discussed in terms of a model that is based on the formation of a defect band along the grain boundaries in the vicinity of the Fermi level.