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

The effects of H coverage θH 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 Ts=450–800 °C, held at the growth temperature for 30 s, cooled to <200 °C, and then exposed to atomic deuterium until saturation coverage. D2 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 Ts and x. In contrast to solid-source MBE films grown in this temperature regime, Ge segregation during GS-MBE decreases with decreasing Ts due to the increasing H coverage. The results were well described by a model accounting for the Si/Ge site exchange and θH. The Ge segregation enthalpy varies from −0.28 eV at Ts⩾800 °C, where the steady-state hydrogen coverage θH approaches zero, to −0.10 eV at Ts⩽450 °C, where θH is nearly saturated.