Measurements of alloy composition and strain in thin Ge_xSi _1-x layers

Abstract

The utility of Raman spectroscopy for the simultaneous determination of composition and strain in thin GexSi1-x layers has been investigated. Using data from the literature and new data for the strain shift of the Si-Si phonon mode presented here, we show how Raman spectra provide several different means of measuring composition and strain in samples as thin as 200 Å. We demonstrate that for largely relaxed layers with compositions near x=0.30, Raman scattering can measure the composition, x, with an accuracy of ±0.015 and the strain, ε, with an accuracy ±0.0025. The accuracy of the alloy composition obtained from Raman spectra is comparable or, in the case of very thin layers, superior to that measured by other techniques such as x-ray diffraction, electron microprobe, and Auger electron spectroscopy.