▪ Abstract New classes of Sn-containing group IV semiconductors are described. Novel CVD routes lead to growth of a broad range of Ge1−ySny alloys and compounds directly on Si substrates. The direct bandgap (E0) and optical transitions E0+Δ0, E1, E1+Δ1, E0′, and E2 of Ge1−ySny exhibit strong nonlinearities in the compositional dependence, and their bowing parameters correlate with those in Ge1 −xSix, suggesting a scaling behavior for the electronic properties. The Ge1−ySny films can be used as “virtual substrates” for the subsequent growth of Ge1−x−ySixSny ternaries. These are created for the first time and exhibit unprecedented thermal stability, superior crystallinity and unique optical and strain properties such as adjustable bandgaps, and controllable strain states (compressive, relaxed, and tensile). The synthesis of Ge1−x−ySixSny makes it possible to decouple strain and bandgap and adds new levels of flexibility to the design of group IV devices. The Ge-Si-Sn system also represents a new class of “d...

TIN-BASED GROUP IV SEMICONDUCTORS: New Platforms for Opto- and Microelectronics on Silicon

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.

Dielectric function spectra of strained and relaxed Si1−xGex alloys (x=0–0.25)

The effect of the carbon content on the optical transitions of Si1−yCy layers grown pseudomorphically on Si(001) substrates was investigated by spectroscopic ellipsometry and electroreflectance spectroscopy for 0≤y≤0.012 in the energy range between 3 and 5 eV. The ellipsometry data show a decrease of the slope of the dielectric function near the critical points and a tendency of a critical point shift with increasing carbon content. This shift was analyzed by measuring and fitting electroreflectance spectra at 80 K, resulting in a weak and linear dependence on the carbon content at all transitions. The E1 critical point energy increases with an increasing carbon content while the E2 energy decreases, both at a rate of about 30 meV/%[C]. The E’0 transition decreases at a smaller rate of about 20 meV/%[C]. The results are discussed in the light of previous discussions and a simple estimate based on silicon deformation potentials.

Optical transitions in strained Si1−yCy layers on Si(001)

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.

Spectroscopic ellipsometry of Si1−xGex epilayers of arbitrary composition 0≤x≤0.255

In-situ dual-wavelength and ex-situ spectroscopic ellipsometry studies of strained SiGe epitaxial layers and multi-quantum well structures

Spectroscopic ellipsometry has been used to study thick, relaxed and thin, strained epilayers of Si1−xGex on Si in the range 0.1<x<0.25. Dielectric functions of relaxed Si0.87Ge0.13 and Si0.8Ge0.2 have been obtained and long‐wavelength absorption coefficient values, required for interference fringe fitting, shown to be higher than measured previously. The dielectric function of strained Si0.78Ge0.22 has been measured for the first time and the effects of strain on the critical points shown to be consistent with deformation potential theory. An interpolation procedure has been developed for the fitting of layer composition and thickness, and excellent agreement with conventional techniques obtained for a series of uncapped single epilayers. The surface roughness of Si1−xGex epilayers has been studied as a function of time and deposition temperature and shown to play an important role in the modeling. The application of the technique to the characterization of buried strained layers is discussed.

Spectroscopic ellipsometry characterization of strained and relaxed Si1-xGex epitaxial layers

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Spectroscopic ellipsometry characterization of strained and relaxed Si1-xGex epitaxial layers