Strained Si Thin Film Research Articles

Atomic-scale Ge diffusion in strained Si revealed by quantitative scanning transmission electron microscopy

Aberration-corrected scanning transmission electronmicroscopy is employed to investigate the local chemistry in the vicinity of a Si0.8Ge0.2/Si interface grown bymolecular-beamepitaxy.Atomic-resolution high-angle annular dark field contrast reveals the presence of a nonuniform diffusion of Ge from the substrate into the strained Si thin film. On the basis of multislice calculations, a model is proposed to quantify the experimental contrast, showing that the Ge concentration in the thin film reaches about 4% at the interface and decreases monotonically on a typical length scale of 10 nm. Diffusion occurring during the growth process itself therefore appears as a major factor limiting the abruptness of interfaces in the Si-Ge system

Si0.5Ge0.5 bulk single crystals with uniform composition

Compositionally uniform 10mm diameter Si0.5Ge0.5 bulk crystals were grown by the traveling liquidus-zone (TLZ) method which we developed for the alloy crystal growth. Axial compositional variation was less than 0.5at% for the length of 12mm and radial one was less than 0.3at% and showed excellent compositional uniformity. The average full width at half maximum of X-ray rocking curves for 004 diffraction measured across a disk is less than 36arcsec (0.01°) at a distance of 3.5mm away from the seed/crystal interface. This shows high crystallinity and promise of TLZ-grown crystals as substrates for CMOS devices using n-channels of strained Si thin films and p-channels of strained Ge thin films.

Application of SiGe bulk crystal as a substrate for strain-controlled heterostructure materials

We report on combination of crystal growth of bulk SiGe and thin film crystals on SiGe bulk substrates to prepare heterostructures with controlled stain in constituent materials. Muticomponent zone melting method to permit crystal growth with uniform composition and Czochralski growth were employed as growth techniques for SiGe bulk crystals. On homemade SiGe bulk substrates, we realized strained Si thin film as well as luminescent strained quantum wells with improved structural perfection compared with those on relaxed SiGe on commercially available Si.

Compact Analytical Threshold-Voltage Model of Nanoscale Fully Depleted Strained-Si on Silicon–Germanium-on-Insu lator (SGOI) MOSFETs

In this paper, a physically based analytical threshold-voltage model is developed for nanoscale strained-Si on silicon-germanium-on-insulator MOSFETs for the first time, taking into account short-channel effects. The model is derived by solving the 2-D Poisson equation in strained-Si and SiGe layers. The effects of various important device parameters like strain (Ge mole fraction in the SiGe layer), body doping, gate workfunction, strained-Si thin film and SiGe layer thickness, etc., has been considered. We have demonstrated that increasing strain in order to enhance device performance can lead to undesirable threshold-voltage rolloff. The model is found to agree well with the 2-D simulation results

Suppression of Structural Imperfection in Strained Si Thin Film by Utilizing SiGe Bulk Substrate

We demonstrate suppression of structural imperfection in strained Si by utilizing homemade SiGe bulk crystal as a substrate. X-ray reciprocal space mapping clarified that the growth of a Si thin film on a SiGe bulk substrate leads to reduction in the orientation fluctuation compared with that on a SiGe virtual substrate. Furthermore, analysis of Raman spectra revealed dramatic decrease of the strain fluctuation in the strained Si film on the SiGe bulk substrate. These results suggest that the SiGe bulk crystal can be utilized as a substrate for various strain-controlled heterostructures for fundamental studies as well as improvement of device performance.

Phosphorus Donors in Highly Strained Silicon

The hyperfine interaction of phosphorus donors in fully strained Si thin films grown on virtual Si(1-x)Ge(x) substrates with x< or =0.3 is determined via electrically detected magnetic resonance. For highly strained epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly below the limit predicted by valley repopulation. Within a Green's function approach, density functional theory shows that the additional reduction is caused by the volume increase of the unit cell and a relaxation of the Si ligands of the donor.

Fabrication of dislocation-free tensile strained Si thin films using controllably oxidized porous Si substrates

A method to fabricate strained Si films is reported via the oxidation of a thin Si film on a porous Si substrate. The Si film can be put under tensile stress in a controllable fashion through the expansion of the porous Si upon low temperature oxidation. The thin Si layer on porous Si substrate can be fabricated using a self-limiting anodization of epitaxially grown intrinsic Si on a heavily doped p-type Si substrate. Tensile strain of up to ∼1% is observed in 100nm thick Si films, making it suitable for the various device applications based on strained Si.

Suppression of Structural Imperfection in Strained Si Thin Film by Utilizing SiGe Bulk Substrate

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Composition and stress analysis in Si structures using micro‐raman spectroscopy

Strained silicon (Si) technology enables improvements in complementary metal oxide semiconductor (CMOS) performance and functionality via replacement of the bulk, cubic-crystal Si substrate with an Si substrate that contains a tetragonally distorted, biaxially strained Si thin film at the surface. Here we use Raman spectroscopy to allow us to characterise growth processes of strained si, and to characterise the resulting level of strain/stress in the si and the effect it has on the underlying layer of graded SiGe.