GE PROFILE FROM THE GROWTH OF SIGE BURIED LAYERS BY MOLECULAR-BEAM EPITAXY

X-ray photoelectron spectroscopy measurements were obtained and interpreted by a kinetic simulation to determine the germanium concentration profile of thin Si/SiGe heterostructures grown at 500-degrees-C using elemental source molecular beam epitaxy. The primary finding is that there are significant segregation effects in these commonly grown structures which affect both the "leading" and "trailing" interfaces. Upon opening of the germanium shutter, the surface monolayer must be built up to a germanium composition of greater than 96% before the composition of the deposited alloy layer is equal to the flux composition for a Ge ratio of 0.3. This buildup causes the germanium depletion at the leading interface. Upon termination of the germanium flux, the incorporation of the germanium rich monolayer into the growing silicon cap layer causes a corresponding degradation of the trailing interface.