We demonstrate that the crystalline quality of Si layers grown on sapphire substrate (SOS) by the CVD method can be greatly improved through the use of implantation of Si ions and subsequent thermal annealing at relatively low temperatures (∼550 °C). This method utilizes an amorphous layer created by ion implantation near the sapphire/Si interface. Subsequent regrowth of this amorphous layer starting from the relatively perfect Si surface region leads to a much improved Si crystalline layer, as evidenced by MeV 4He+ channeling and TEM measurements. When the implantation-formed amorphous layer is located at the outer portion of the Si layer, thermal annealing leads to only a small reduction in the amount of defects in the regrown layer as compared to the unimplanted sample. In these layers, epitaxial regrowth occurs with the same rate and activation energy observed in self-ion-implanted 〈100〉 Si.
We have carried out an extensive Raman-scattering investigation of the structure of berylliumimplanted gallium arsenide. Single-crystal GaAs was bombarded with 45-keV Be ions, and backscattering Raman measurements were made, prior to any anneal, as a function of ion fluence, laser photon energy, and depth (via chemicalwtch removal of surface layers). Line-shape and intensity analyses of the observed Srst-order Raman spectra, especially of the longitudinalwptical-(LO) phonon line (which is superimposed on the broad spectral signature of amorphous GaAs), support a structural model of the implantation-induced damage layer as a Sne-scale mixture of amorphous and crystalline GaAs. The etch studies yield a structural depth pro61e in terms of the depth dependence of the amorphous volume fraction (derived from measured scattering intensities) and of the characteristic crystaOite size. The first 1500 A is a high-damage layer having nearly constant structure; this is foBowed by a structurally graded transition region in which the crystalline volume frac-0 tion and the crystaBite size smoothly increase until the bulk crystal is reached at about 4000 A, For a fluence of 5)&10' ions/cm, the near-surface high-damage plateau is characterized by an amorphous volume fraction of 0.25 and a crystallite size of 60 A. This plateau begins at the surface; there is no evidence of the near-surface decrease in disorder which appears in some commonly used theoretical simulations. Varying the laser photon energy from 1.55 to 2.71 eV reveals that the LO intensity (arising from the crystalline component) increases at both ends of this spectral range. The intensity increase at low photon energies rejects the increasing optical penetration depth C, 'i. e. , effective scattering volume), but the increase at high photon energies signi5es a real rise in the scattering eSciency. We interpret this as a resonance-Raman elect associated with the approach toward the El interband transition. This resonance is partially quenched as the crystallite size is decreased for heavily implanted samples. The combination of Raman scattering with chemical-etch removal of nearsurface layers has not been previously exploited, and this approach is emphasized in the present investigation. The effectiveness of this approach is demonstrated by our results, especially with respect to the determination of
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