Sb surfactant-mediated epitaxy of Ge on Si(113) studied by AFM, SEM and GIXRD
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Sb surfactant-mediated epitaxy of Ge on Si(113) studied by AFM, SEM and GIXRD T. Clausen, J. I. Flege, Th. Schmidt, and Jens Falta Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee, 28359 Bremen, Germany ABSTRACT We have investigated the Sb surfactant-mediated growth of Ge on Si(113) over the temperature range from 500◦ C to 700◦ C. The surface morphology, film thickness, interface roughness and strain state of the films have been determined by the use of scanning electron microscopy, atomic force microscopy and grazing incidence x-ray diffraction. After growth at temperatures between 500◦ C and 600◦ C smooth Ge films have been observed, which show a partial strain relaxation. However, increasing the temperature to 700◦ C, a rough surface with a high density of three-dimensional islands has been found. INTRODUCTION The combination of silicon technology with thin epitaxial germanium layers for microelectronical applications is a long standing goal in semiconductor physics. To overcome the problem of Stranski-Krastanov growth resulting from the lattice mismatch of both species [1], graded buffer layers [2] and surfactant-mediated epitaxy (SME) [3, 4] can help to realize smooth two-dimensional Ge layers. Moreover, SME has the advantage that Si-Ge interdiffusion is suppressed [5] and thus atomically sharp Si-Ge interfaces can be achieved. We have chosen the Si(113) surface as a substrate, which is one of the thermally stable high-index surfaces of silicon. From a crystallographic point of view it is located in between the technologically relevant Si(001) surface and the Si(111) surface. For the latter, SME has successfully been established [6, 7]. Using antimony (Sb) as a surfactant, two-dimensional Ge growth has been achieved, in which an ordered dislocation network at the Si-Ge interface reduces the strain [4, 6]. Within this contribution we report on a combined real-space and reciprocal-space study on Sb surfactant-mediated epitaxy of Ge on Si(113) over a temperature range from 500 ◦ C to 700◦ C. In order to investigate the surface morphology, we used atomic force microscopy (AFM) and scanning electron microscopy (SEM), whereas the strain state of the Ge films was probed by grazing incidence x-ray diffraction (GIXRD), which in addition is well suited for the analysis of the average surface and interface morphology [7]. EXPERIMENTAL DETAILS The sample preparation was performed in an ultra-high vacuum system (base pressure below 1×10−9 mbar). After RCA cleaning [8] and degassing the Si(113) substrates for at least 16 hours at 600◦ C, one or two short flashes up to around 890◦ C led to a clean Si(113)-(3×2) reconstruction of the surface. Heating of the samples was performed by passing a direct current through them, while the temperature was monitored with an infra-red pyrometer. Sb and Ge were evaporated from Knudsen cells at different sample temperatures in the range from 500 ◦ C to 700◦ C. After
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saturation of the Si(113) surface with Sb, Ge was evaporated while t
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