Open Access

The study is concerned with the effect of short-term high-temperature heating on Si:Se and Si:S samples, whose surface layers are doped with phosphorus to high concentrations. It is found that the resistivity of the wafers substantially increases deep in the bulk within up to similar to 10 mu m. The experimental data suggest that this effect is due to enhanced diffusion of chalcogen in the presence of the phosphorus-doped surface region. The mechanism of the effect is the injection of nonequilibrium interstitial silicon atoms from the layer heavily doped with phosphorus to the bulk of the sample. This results in a shift of the equilibrium between the concentrations of substitutional and interstitial impurity atoms towards higher concentrations of interstitials and, as a consequence, towards the increase in the relative content of the fast-diffusing interstitial component of the impurity.

The mechanisms of femtosecond laser-induced transient melting and atomic mixing in a target composed of a 30 nm Au film deposited on a bulk Cu substrate are investigated in a series of atomistic simulations. The relative strength and the electron temperature dependence of the electron-phonon coupling of the metals composing the layered target are identified as major factors affecting the initial energy redistribution and the location of the region(s) undergoing transient melting and resolidification. The higher strength of the electron-phonon coupling in Cu, as compared to Au, results in a preferential sub-surface heating and melting of the Cu substrate, while the overlaying Au film largely retains its original crystalline structure. The large difference in the atomic mobility in the transiently melted and crystalline regions of the target makes it possible to connect the final distributions of the components in the resolidified targets to the history of the laser-induced melting process, thus allowing for experimental verification of the computational predictions. (C) 2009 Elsevier B. V. All rights reserved.