Si and Si1-xGex molecular beam epitaxial growths have been conducted with and without 10(-3) Pa atomic hydrogen (AH) overpressure to observe the effect of AH on surface morphology. Si1-xGex (x=0.1 and 0.2) layers 3 nm thick grown at 710 degrees C without AH showed flat epitaxy by transmission electron microscopy but identical layers grown in the presence of AH showed interface stress undulations. Stress undulations were also observed for a 20% Ge alloy grown with AH at 600 degrees C. For 30% Ge alloy layers grown at 710 degrees C, undulations were seen both with and without AH with a approximate to 250 nm period, however the amplitudes of the undulations were greater with AH. Low energy electron diffraction investigation of Si homoepitaxy revealed,at growth temperatures between 600 and 800 degrees C, improved epitaxy with 100 s of 10(-3) Pa AH. In combination, these results are evidence that AH has increased the adatom mobility.