Microscopic Study of Si-Ge Heteroepitaxial Growth by STM/STS

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Heteroepitaxially grown films have much potentials to achieve innovative devices. A Si-Ge superattice structure is one of the most attractive candidates But the strain nduced by a 4.2% lattce mismatch between Si and Ge makes the growth complicated, and then Ge-covered surfaces become rough, causing the non-abruptness of the superlattice In this study, the surface topotraphy and the surface electronic states of Ge overlayrs on Si(001) were investigated by a UHB-STM/STS.Ge atoms were deposited on Si(001) at substrate temperatures of 300, 400 and 500ﾟC by the amount from less than IML to 8ML.The deposited Ge atoms dimerize on Si(001). At a coverage higher than IML, the missing dimer rows are introduced in the Ge overayr exhibiting belt or patch structures. The hut clusters with 4 facets of {015} planes grow after the Ge deposition of 3ML, and the hut clusters coalesce at 300ﾟC after the whole surface is covered with the custers. The GROWTH MODE IS CHANGED AT 400ﾟC, where the macroscpic clusters with 4 facets of {113} planes grow at higher than 5ML.At 500ﾟC another type of macroscopic clusters ike a dome grows an 6.5ML.Annealing effects at 500ﾟCfor 5min were also investigated for the 5ML Ge overlayr grown at 400ﾟC.Complircated clusters grow, with the {015} facets on the foot of the clusters, the {113} facets on the breast, and the 2x1 reconstructed (001) surface with many steps on the top. The hut clusters disappear by the annealing as if the macroscopic clusters absorb the hut clusters, then are transformed into the complicated clusters. After the hut clusters disappear, the patch structures rcappear between the complicated clusters. The layr with the patch structures may by strongly connected to the substrate, and the hut custer may be loosey bound to the substrate. The stability of the {015} surface close to te interface was discussed.