▪ 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

This feature article presents an overview of a study of several different aromatic-functionalized amphiphilesfatty acid and phospholipid derivatives. These amphiphiles form organized assemblies when the fatty acids are spread as monolayers at the air−water interface or when the phospholipids are dispersed in aqueous solutions. For a wide range of aromatic chromophorestrans-stilbene derivatives and a series of “vinylogues” (1,4-diphenyl-1,3-butadiene and 1,6-diphenyl-1,3,5-hexatriene), diphenylacetylenes, and azobenzenes such as phenyl, biphenyl, and terphenyl derivatives and modified stilbenes (styryl thiophenes and styryl naphthalenes)assembly formation is accompanied by formation of aggregates of the aromatic groups. Results of experimental studies and simulations indicate that in many cases the aromatics form a small, stable “unit aggregate” characterized by strong “noncovalent” edge-to-face interactions among adjacent aromatics. Although the unit aggregates exhibit characteristic spectral shifts and s...

Self-Assembly of Aromatic-Functionalized Amphiphiles: The Role and Consequences of Aromatic−Aromatic Noncovalent Interactions in Building Supramolecular Aggregates and Novel Assemblies

Photoluminescence of strained Si1−x−yGexCy alloys grown by rapid thermal chemical vapor deposition on Si(100) is investigated Two dominant features are reported: At low pump intensities, the photoluminescence is dominated by a deep level broad luminescence peak around 800 meV whereas at high pump intensities, a well‐resolved band‐edge luminescence (no phonon and transverse optic replica) is observed At 77 K, we attribute this band‐edge feature to an electron‐hole plasma luminescence of the ternary alloy The dependences of the deep level and band‐edge peaks versus the excitation power density are, respectively square‐root‐like or superlinear A blue shift of the energy gap of Si1−x−yGexCy alloys with respect to Si1−xGex alloy is observed The blue shift increase with carbon content corresponds to what is expected for the bulk alloy An eventual influence of the strain relaxation cannot be excluded

Band‐edge and deep level photoluminescence of pseudomorphic Si1−x−yGexCy alloys

Germanium-silicon epitaxial layers are now being applied in a variety of heterojunction devices on silicon substrates. In this paper, I review the growth of these structures by chemical vapor deposition. While a wide variety of growth conditions have been used, there is a general trend toward low temperature processes where surface chemical reactions play a dominant role. The present understanding of the decomposition of various reactants is therefore reviewed, followed by a discussion of the implications for growth kinetics. The introduction of defects during growth will also be discussed. Finally a summary of recent device developments will be given.

Growth of epitaxial germanium-silicon heterostructures by chemical vapour deposition

We report a new photoluminescence process in epitaxial Si1−xGex layers grown on Si by rapid thermal chemical vapor deposition which we attribute to the recombination of excitons localized at random alloy fluctuations. This luminescence is characterized by saturation at very low excitation densities (≂100 μW cm−2), very long decay times (≳1 ms), and high quantum efficiency at low excitation. We have directly measured an external photoluminescence quantum efficiency of 11.5±2%.

High quantum efficiency photoluminescence from localized excitons in Si1−xGex

The systematic study of band‐edge luminescence in pseudomorphic Si/Si1−xGex/Si double‐heterostructure layers is reported for a wide composition range, 0.12<x<0.24, for the first time. An analytical expression for the exciton energy gap at 4.2 K valid for x<0.24 is derived from the no‐phonon line energies: ESX(x) = 1.155−0.874x+0.376x2 eV. Addition of an expression for the exciton binding energy provides an approximation for the energy difference between the alloy valence band and the lowest conduction‐band edge at low temperature. An exciton upshift of 16.9 meV due to quantum confinement is observed in a 6.3‐nm Si0.83Ge0.17 alloy well. This is consistent with either type‐I or type‐II band alignment for which the conduction‐band offset has a magnitude ‖ΔEc‖ ≤ 10 meV. The excitonic hole is closely confined in the alloy but the spectra suggest that the electron density in the silicon barriers is increased for the thin layer.

Near‐band‐gap photoluminescence from pseudomorphic Si1−xGex single layers on silicon

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

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

Spectroscopic ellipsometry of Si1-xGex multi-quantum wells

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Near‐band‐gap photoluminescence from pseudomorphic Si1−xGex single layers on silicon

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

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

Spectroscopic ellipsometry of Si1-xGex multi-quantum wells