In this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin silicon on insulator (SOI) substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced in to the upper SiGe material, which appeared dislocation free to the limit of the cross sectional transmission electron microscopy analysis. We thus have a method for producing very low dislocation, relaxes SiGe films with the additional benefit of an SOI substrate.

Wetteroth, T.; Wilson, S. R.; and Powell, Adrian R., "Carrier concentration and lattice absorption in bulk and epitaxial silicon carbide determined using infrared ellipsometry" (1999 Carrier concentration and lattice absorption in bulk and epitaxial silicon carbide determined using infrared ellipsometry We have measured the dielectric function of bulk nitrogen-doped 4H and 6H SiC substrates from 700 to 4000 cm Ϫ1 using Fourier-transform infrared spectroscopic ellipsometry. Photon absorption by transverse optical phonons produces a strong reststrahlen band between 797 and 1000 cm Ϫ1 with the effects of phonon anisotropy being observed in the region of the longitudinal phonon energy ͑960 to 100 cm Ϫ1 ͒. The shape of this band is influenced by plasma oscillations of free electrons, which we describe with a classical Drude equation. For the 6H-SiC samples, we modify the Drude equation to account for the strong effective mass anisotropy. Detailed numerical regression analysis yields the free-electron concentrations, which range from 7ϫ10 17 to 10 19 cm Ϫ3 , in good agreement with electrical and secondary ion mass spectrometry measurements.Finally, we observe the Berreman effect near the longitudinal optical phonon energy in nϪ/nϩ homoepitaxial 4H SiC and hydrogen implanted samples, and we are able to determine the thickness of these surface layers.

No abstract

A model is presented for a possible mechanism of screw dislocation (including micropipe) nucleation in silicon carbide. The model is based on the observation of micropipe nucleation at the sites of foreign material inclusions using synchrotron white beam x-ray topography and transmission optical microscopy. It is shown that incorporation of the inclusion into the growing crystal can lead to deformation of the protruding ledge which constitutes the overgrowing layer. Accommodation of this deformation into the crystal lattice leads to the production of pairs of opposite sign screw dislocations which then propagate with the growing crystal. Evidence for the existence of such pairs of dislocations is presented.

No abstract