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 g as-source molecular beam epitaxy (GS-MBE) were investigated using D2 t emperature 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, h eld at the growth temperature for 30 s, cooled to <200 degrees C, and then exposed to atomic deuterium until saturation coverage. D-2 TPD sp ectra were fit using four peaks corresponding, in order of decreasing activation energy, to desorption from Si monodeuteride, Ge-Si mixed-di mer 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 tempe rature regime, Ge segregation during GS-MBE decreases with decreasing T, due to the increasing H coverage. The results were well described b y a model accounting for the Si/Ge site exchange and BH. The Ge segreg ation enthalpy varies from -0.28 eV at T-s greater than or equal to 80 0 degrees C, where the steady-state hydrogen coverage theta(H) approac hes zero, to -0.10 eV at T-s less than or equal to 450 degrees C, wher e theta(H) is nearly saturated. (C) 1997 American Institute of Physics .