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Scanning tunneling microscopy studies of Ge/Si films on Si(111): From layer by layer to quantum dots

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8 Author(s)
Motta, N. ; Istituto Nazionale di Fisica della Materia, Dipartimento di Fisica, Università di Roma Tor Vergata, 00133 Roma, Italy ; Sgarlata, A. ; Calarco, R. ; Castro Cal, J.
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We have followed by scanning tunneling microscopy (STM) the growth of thin Ge films obtained by reactive deposition epitaxy on the Si(111) surface kept at 500 °C. For Ge thickness smaller than 0.45 monolayers (ML), STM images show large 7×7 flat regions without protrusions while at higher coverages flat, triangular 5×5 islands start nucleating. We have followed the evolution of this wetting layer up to its completion and investigated its surface composition at 3 ML by current imaging tunneling spectroscopy measurements. At larger coverages thick Ge islands (quantum dots) start to nucleate according to the Stranski-Krastanov mechanism. We analyze the evolution of the lattice strain both on the wetting layer and on the islands up to 15 ML coverage. A clear expansion of the lattice parameter as a function of the coverage is evidenced both on the islands’ top and on the wetting layer. The luminescence yield measured at 10 K on samples covered by 40 Å of Ge and capped with 10 Å of Si evidences a structure that could be assigned to Ge quantum dots. © 1998 American Vacuum Society.

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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:16 ,  Issue: 3 )