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.