20Congreso Nacional 
Sociedad Mexicana de Ciencia de Superficies y Vacío A.C.

Atomic-Level Control During Film Growth Under Highly Kinetically Constrained Conditions: H-Mediation and Ultra-High Doping in Si1-xGex Gas-Source MBE

Joe Greene
Frederick Seitz Materials Research Laboratory
and the Materials Science Dept., University of Illinois, USA
Univ. of Illinois, Urbana 61801, Illinois, USA

 Surface reaction pathways and kinetics of Si1-xGex growth on Si(001) by gas-source MBE (GS-MBE), CVD, and atomic-layer epitaxy (ALE) from Si2H6/Ge2H6 mixtures have been investigated using a combination of in-situ RHEED, EELS, STM, STS, TPD, and AES together with post-deposition TEM, HR-XRD, XTEM, and electronic transport measurements. Film growth data are well described by models containing separate reaction steps for dissociative chemisorption, surface reactions, and hydrogen desorption. For UV-photostimulated ALE, hydrogen termination provides internally self-limiting kinetics and allows epitaxial growth at room temperature and below.
 The results of isotopically-tagged D2 temperature-programmed desorption (TPD) experiments were used to model temperature-dependent H-mediated effects of high B coverages on the growth kinetics of B ultra-high doped Si1-xGex(001), up to 1.5x1022 cm-3 (30 at%!!), through changes in B-induced surface reconstruction and back-bond charge transfer, and to determine Ge segregation kinetics as a function of x and steady-state H coverage during GS-MBE. Excess incorporated B does not precipitate out of solution as commonly supposed. Rather, our recent NEXAFS and HR-XRD results, carried out at the Synchrotron Radiation Center in Stoughton, show it is incorporated as sp2 bonded dimers with trigonal symmetry on substitutional Si sites. The dimers are bond-saturated and thus electrically neutral. Further, they have very low charge scattering cross-sections.


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