Transition of carbon binding states on Si(100) depending on substrate temperature and its effect on Ge growth

Effect of binding states of carbon (C) with Si substrate on Ge growth was studied. The samples were prepared by solid-source molecular beam epitaxy system with electron beam gun for C sublimation and K-cell for Ge evaporation. The C binding states to Si(100) surface evaluated by XPS measurement revealed a transition of the fraction of C-C and Si-C bonds depending on carbon deposition temperature (T-C). The fraction of C-C bonds was major below T-C = 600 degrees C and was almost equal to that of Si-C bonds at T-C = 800-1000 degrees C. Surface roughening by the c(4 x 4) reconstruction induced by a large amount of Si-C bonds was observed at T-C = 1000 degrees C. Ge equivalent to 10-nm thick was deposited on C/Si substrate at 550 degrees C. Amorphous Ge layers were grown for T-C = 200-800 degrees C because Ge adatoms nucleated on the C-C structure dominantly. Structural transition from 2-D films to dome-shaped 3-D dots occurred for T-C = 1000 degrees C due to the increase of Ge diffusion length by the Si-C structure. Concerning the dependence of C coverage, the crystallinity of Ge film deteriorated with increasing C coverage for T-C = 200 degrees C due to the increase of C-C structure which enhances the formation of amorphous Ge. On the other hand, crystallinity of Ge dots were improved with C coverage and were saturated over 0.2 ML for T-C = 1000 degrees C. This reflects the enlargement of dots due to C-suppressed Ge growth induced by Si-C bonds at the surface. (C) 2013 Elsevier B.V. All rights reserved.