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 film 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.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)