Dielectric function spectra for strained and relaxed Si1−xGex alloys with x∼0.13 and 0.20 are presented in numerical form. The effect of strain is shown to cause a modification of the spectra in the E1 critical point region, resulting in a decrease in refractive index at 1.96 eV, amounting to 0.06 at x=0.22. The spectral dependence of the refractive index is presented for a series of strained layers. An overview is given of spectral databases and the single-wavelength ellipsometry data available in the literature.

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Spectroscopic ellipsometry has been used to study thick, relaxed and thin, strained epilayers of Sil-,Ge, on Si in the range 0.1

An enhancement of the infrared detection efficiency of Si photon-counting detectors by inclusion of SiGe absorbing layers has been demonstrated for what is believed to be the first time. An improvement of 30 times in detection efficiency at a wavelength of 1210 nm compared with that of an all-Si structure operated under identical conditions has been measured. The Si/Si(0.7)Ge(0.3) device is capable of room-temperature operation and has a response time of less than 300 ps.

Critical point (CP) transition energies have been calculated for strained Si1−xGex (0≤x≤0.255) between 2.5 and 3.5 eV from Lorentzian fits to the second differential of reference dielectric function spectra. E1 and E′0 transition energies are similar to those of the relaxed alloy. Comparison with deformation potential theory shows E1+Δ1 to be coincident with E′0 due to a strain-induced up shift in the former’s transition energy. The reference spectra and CP transition energies are used in an interpolation procedure to analyze spectroscopic ellipsometry spectra of both uncapped and buried layers of strained Si1−xGex. Compositions and thicknesses are obtained in good agreement with alternative techniques.