Raman-scattering elucidation of the giant isotope effect in hydrogen-ion blistering of silicon.
In this work, we investigate the origin of a giant isotope effect discovered in the blistering of hydrogen-ion-implanted and annealed silicon. Si(001) samples were implanted or co-implanted with 5 keV of H and/or D ions to total fluences of 2 x 10(16) and 6 x 10(16) ion/cm(2). The lower fluence is sufficient for blistering by pure H, but the higher one is required for the maximum blister coverage whenever D is involved. On these samples, we carried out Raman-scattering investigations of the evolution of Si-H/D complexes upon a stepwise thermal annealing from 200 to 550 degrees C. We have identified the critical chemical transformations characterizing the hydrogen-deuterium-induced blistering of silicon. The puzzling dependence on ion mass appears to be mainly connected with the nature of the radiation damage. We have found that H is more efficient in "preparing the ground" for blistering by nucleating platelets parallel to the surface, essentially due to its ability to agglomerate in the multihydride monovacancy complexes that evolve into hydrogenated extended internal surfaces. By contrast, D is preferentially trapped in the surprisingly stable monodeuteride multivacancies.
Si-H stretch modes of hydrogen-vacancy defects in silicon
Abstract The Si H stretch modes in proton-implanted crystalline silicon have been studied by FTIR spectroscopy. From the annealing behaviour and dose dependence of the stretch-mode intensities, it is found that one complex gives rise to modes at 2121 and 2144 cm −1 , a second to modes at 2166 and 2191 cm −1 , and a third to a single mode at 2222 cm −1 . The isotope shifts of these centres have been obtained from measurements on samples implanted with protons and deuterons. Moreover, the symmetries of the centres have been determined from uniaxial stress measurements. We assign the 2121 and 2144 cm −1 modes to VH 2 , the 2166 and 2191 cm −1 modes to VH 3 , and the 2222 cm −1 mode to VH 4 . Another mode at 2068 cm −1 is tentatively ascribed to VH. The Si H and Si D stretch modes of VH n D m ( n + m ≤ 4) have been calculated with a simple model which has been used to fit all the experimental frequencies. The agreement between fitted and observed frequcies is excellent.
Ab initio quantum dynamics of H2Si(100) adsorption/desorption on a 3-D potential
Abstract Hydrogen adsorption on the Si(100)2 × 1 transforms the buckled Si dimers of the reconstructed surface into symmetric monohydride units. The dynamics of adsorption is therefore coupled to lattice dynamics. Based on the results of ab initio calculations, we study the dynamics of both adsorption and desorption for the coupled molecule + surface system in a coupled channel approach. We find that the desorption barrier is not only reflected in the energy of the desorbing molecules, but also transferred to lattice excitations. In adsorption thermal excitations of the surface help to overcome the barrier and thus increase the sticking coefficient at elevated surface temperatures. As has been pointed out earlier, a dynamical mechanism with such features could help to understand discrepancies between experimental results for the H 2 Si (100) system that are hard to reconcile otherwise.