Effects of H coverage on Ge segregation during Si1-xGex gas-source molecular beam epitaxy

The effects of H coverage theta(H) on Ge segregation during Si1-xGex gas-source molecular beam epitaxy (GS-MBE) were investigated using D2 temperature programmed desorption (TPD). Si1-xGex films with x = 0.01-0.30 were grown from Si2H6/Ge2H6 mixtures at T-s = 450-800 degrees C, held at the growth temperature for 30 s, cooled to <200 degrees C, and then exposed to atomic deuterium until saturation coverage. D-2 TPD spectra were fit using four peaks corresponding, in order of decreasing activation energy, to desorption from Si monodeuteride, Ge-Si mixed-dimer monodeuterides, Si dideuteride, and Ge monodeuteride. Steady-state Ge surface coverages were determined from the TPD data as a function of T, and x. In contrast to solid-source MBE films grown in this temperature regime, Ge segregation during GS-MBE decreases with decreasing T, due to the increasing H coverage. The results were well described by a model accounting for the Si/Ge site exchange and BH. The Ge segregation enthalpy varies from -0.28 eV at T-s greater than or equal to 800 degrees C, where the steady-state hydrogen coverage theta(H) approaches zero, to -0.10 eV at T-s less than or equal to 450 degrees C, where theta(H) is nearly saturated. (C) 1997 American Institute of Physics.