Vacancy-type defects in strained-Si layers deposited on Si0.75Ge0.25/graded-SiGe/Si structures were probed by using mono-energetic positron beams. The Doppler broadening spectra of the annihilation radiation and the lifetime spectra of the positrons were measured for samples before and after annealing (800–1050C). For an as-received sample, the defects in the strained-Si layer were identified as vacancy-type defects coupled with Ge. The mean open size of these defects was estimated to be close to that of a divacancy. The line-shape parameter, S, corresponding to the positron annihilation in the strained-Si layers decreased with increasing annealing temperature, but no large change in the positron lifetime was observed. From a comparison between the Doppler broadening profiles for the strained-Si films and those calculated using the projector augmented-wave method, it was found that the number of Ge atoms forming a complex by coupling with a defect increased with increasing annealing temperature. The number was estimated to be three or four after annealing at 1050C. Since the defect complexes were stable even after annealing at such a high temperature, the defects detected by the positrons could be part of chainlike vacancy clusters.

Vacancy-Type Defects in Strained-Si Layers Deposited on SiGe/Si Structures Probed by using Mono-Energetic Positron Beams. A.Uedono, N.Hattori, H.Naruoka, S.Ishibashi, R.Suzuki, T.Ohdaira: Journal of Applied Physics, 2005, 97[2], 023532 (5pp)