Real-time monitoring of steady-state pulsed chemical beam epitaxy by p-polarized reflectance

The structure in the p-polarized reflectance (PR) intensity R-p4(t)-observed under conditions of pulsed chemical beam epitaxy (PCBE) - is modeled on the basis of the four-layer stack: ambient/surface reaction layer (SRL)/epilayer/substrate. Linearization of the PR intensity with regard to the phase factor associated with the SRL results in a good approximation that can be expressed as R-p4 = R-p3 + Delta R-p. R-p3 is the reflectivity of the three-layer stack ambient-epilayer-substrate. Delta R-p describes the properties of the SRL. An explicit relation is derived between Delta R-p(t) and the time-dependent surface concentrations c(h)(t) (h = 1, 2, ..., N) of the constituents of the SRL, which holds for conditions of submonolayer coverage of the surface by source vapor molecules. Under conditions of low temperature PCBE at high flux, the SRL is expected to exhibit nonideal behavior, mandating replacement of the surface concentrations by activities. Also, in this case, the thickness of the SRL must be represented in terms of partial molar volumina V-h. Since the relation between Delta R-p(t) and the activities of reactants, intermediates and products of the chemical reactions driving heteroepitaxial growth is non-linear, the extraction of kinetic parameters from the measured time dependence of the PR signal generally requires numerical modeling. (C) 1998 Published by Elsevier Science B.V. All rights reserved.