The measurement and analysis of epitaxial recrystallization kinetics in ion-beam-amorphized SrTiO 3
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L. A. Boatner Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6056 (Received 16 June 1994; accepted 17 August 1994)
The solid-state epitaxial-regrowth kinetics of ion-beam-amorphized SrTiO3 surfaces annealed in water-vapor-rich atmospheres have been studied using time-resolved reflectivity (TRR). For this material, the conversion of the reflectivity-versus-time data obtained from the TRR measurements to recrystallized depth-versus-time data is more complicated than in systems such as silicon, where the reflectivity can be fit by assuming that the refractive index N (N = n + ik) in the amorphous layer is constant. In SrTiO3, agreement between measurements made directly with Rutherford backscattering spectroscopy (RBS) and those made using TRR can be obtained only when N is permitted to vary within the amorphous layer, with nonzero values for both the real and imaginary components. In some cases, the roughness of the amorphous/crystalline interface must also be considered. Additionally, a model for H2O-enhanced epitaxial regrowth is presented, which is in good agreement with the shape of the depth-versus-time profiles that are obtained from the TRR data.
I. INTRODUCTION In the present study, the kinetics of epitaxially regrowing amorphous layers in Pb-implanted SrTiO3 have been investigated by measuring and analyzing depth-versus-time information (i.e., growth front velocities) obtained from time-resolved reflectivity (TRR) measurements. The Pb-implanted SrTiO3 samples were annealed in atmospheres containing a variety of watervapor concentrations. The experimental details and general results related to the epitaxial regrowth of ion-beam-amorphized near-surface layers on SrTiO3 single crystals were presented in previous work1^3 which shows that water vapor enhances the epitaxial-regrowth kinetics. The kinetics of this process, in fact, were shown to be determined by diffusion of a species associated with water vapor through the amorphous layer and by the associated alteration of the recrystallization rate at the amorphous/crystalline (a/c) interface. The recent studies of Simpson et al.4'5 have used isotopic substitution and SIMS analysis to determine that hydrogen, in fact, is the fastest-diffusing species in amorphous layers in SrTiO3 which are exposed to a water-vapor-rich ambient. It is, therefore, likely that H2O dissociates as it is adsorbed at the outer surface of the sample and that hydrogen then moves through the solid by "hopping" from one oxygen ion to the next. This type of diffusion mechanism has been reported for other oxides.6 Olson and Roth7 have pioneered the use of TRR as a means of determining the instantaneous epitaxialJ. Mater. Res., Vol. 9, No. 12, Dec 1994 http://journals.cambridge.org
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regrowth velocities of ion-implanted amorphous layers on silicon. In these studies, the reflectivity-(/?)-versustime data (i.e., the TRR measurements) are readily converted to recrystallized depth-(x:)-versus-time data because of the fortuitous observatio
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