Ge surface segregation during Si1-xGex(011) gas-source molecular beam epitaxy from Si2H6 and Ge2H6

Ge surface segregation during Si1-xGex gas-source molecular beam epitaxy on Si(0 1 1) was investigated using in situ D-2 temperature programmed desorption (TPD). The Si1-xGex(0 1 1) layers, x = 0-0.20, were grown from Si2H6/Ge2H6 mixtures at temperatures T-s ranging from 475 degreesC to 750 degreesC. Immediately following film growth, the samples were quenched and exposed to atomic D at 250 degreesC until saturation coverage. TPD spectra from Si1-xGex(0 1 1) consist of five second-order peaks due to D, desorption from, in order of decreasing temperature, Si rest-atom and adatom monodeuterides, Si dideuteride, and Ge rest-atom and adatom monodeuteride phases. Temperature-dependent Ge surface coverages theta (Ge), determined from the TPD results, increase sharply with x ranging, at T-s = 550 degreesC, from 0.27 ML with x = 0.04 to 0.74 ML for layers with x = 0.20. For a given film composition, theta (Ge) decreases with decreasing T-s due to the corresponding increase in the fraction f(Si,H) of Si surface atoms terminated with H. From these data, we find that the Ge segregation enthalpy DeltaH(s) for Si1-xGex(0 1 1) varies from -0.18 eV at T-s = 750 degreesC (f(si,H) < 0.003) to -0.09 eV at T-s = 475<degrees>C (f(Si.H) = 0.22). (C) 2001 Elsevier Science B.V. All rights reserved.