Investigation of atomic displacement in isotopically enriched semiconductor multilayer structures induced by ion implantation and solid phase epitaxial recrystallization processes
Synthesis and Properties of Functional Materials
Final Report Abstract
We investigated the ion-beam induced atomic mixing in crystalline and preamorphized Si, Ge, and SiGe by means of isotopically enriched multilayer structures with special emphasis on the temperature and doping dependence of self-atom mixing. Moreover we studied the atomic mixing of preamorphized Ge isotope multilayer structures induced by SPER. Several experimental techniques were applied to determine the intermixing of the isotope structure (SIMS, APT), the structural state of the ion implanted samples (RBS/C, HRTEM), and to follow the SPER process (TRR). Numerical simulations (CT, MD) were applied to describe the experimental results, i.e., to uncover the underlying mechanisms of atomic mixing under various experimental conditions. We found that ion-beam mixing strongly depends on temperature as well as on the structure of the target material. This behavior originates from thermal spikes initiated by the impinging ions. Collision cascades form locally molten regions within the target, which enhances the motion of the affected host atoms. With increasing temperature the volume of these regions increases. The lower melting point and lower thermal conductivity of amorphous compared to crystalline targets results in longer lasting thermal spikes and thus to a stronger mixing. Comparison of experimental and theoretical results on ion-beam mixing in Ge revealed that the atomic mixing in Ge induced by ion implantation is mainly mediated by thermal spikes. No radiation enhanced diffusion is evident under ion irradiation even up to temperatures of 823 K. A doping dependence is not observed. Considering Si, the ion-beam induced atomic mixing is affected both by thermal spikes and radiation enhanced diffusion. The contribution of thermal-spike mixing to the overall atomic mixing was evaluated by means of MD calculations. The radiation enhanced diffusion is described by highly mobile di-interstitials with defect properties reported in the literature. The observed dopant dependence of atomic mixing is explained by differences in dynamic annealing under n- and p-type doping, which alters the injection rate of di-interstitials. Ion-beam-induced atomic mixing in SiGe can be qualitatively explained by the findings obtained from detailed investigations on this effect in Ge and Si. At low temperatures the thermal spike mechanism should dominate, whereas at higher temperatures ion-beam-induced enhanced self-diffusion seems to be the prevailing process of atomic mixing. Finally, our results on atomic mixing induced by solid phase epitaxial recrystallization of germanium confirms theoretical models and atomistic simulations that predict a bond switching and local rearrangement of matrix atoms as the mechanism mediating the SPER process. The small intermixing of about 0.5 nm observed after the SPER process stems from the relaxation of the preamorphized structure.
Publications
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Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures, J. Appl. Phys. 115, 023506 (2014)
M. Radek, H. Bracht, M. Posselt, B. Liedke, B. Schmidt, and D. Bougeard
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Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium, Appl. Phys. Lett. 107, 082112 (2015)
M. Radek, H. Bracht, B. C. Johnson. J. C. MacCallum, M. Posselt, and B. Liedke
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Ion-beam induced atomic mixing in isotopically controlled silicon multilayers, J. Appl. Phys. 120, 185701 (2016)
M. Radek, H. Bracht, B. Liedke,R. Böttger, and M. Posselt
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Ion-beam-induced atomic mixing in Ge, Si, and SiGe, studied by means of isotope multilayer structures, Materials 10, 813 (2017)
M. Radek, B. Liedke, B. Schmidt, M. Voelskow, L. Bischoff, J. Lundsgaard Hansen, A. Nylandsted Larsen, D. Bougeard, R. Böttger, S. Prucnal, M. Posselt, and H. Bracht
