Ge segregation during the growth of a SiGe buried layer by molecular beam epitaxy

Abstract

The germanium concentration profile of thin Si/SiGe heterostructures grown at 500 °C using elemental source molecular beam epitaxy were measured by x-ray photoelectron spectroscopy. The primary finding from these measurements is that there are significant segregation effects in these commonly grown structures which affect both the ‘‘leading’’ and ‘‘trailing’’ interfaces. Kinetic simulations derived from the measurements indicate that upon opening of the germanium shutter for the deposition of a Si0.7Ge0.3 layer, 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. This buildup causes a germanium depletion at the leading interface. Upon termination of the germanium flux, incorporation of the germanium rich monolayer into the growing silicon cap layer causes a corresponding degradation of the trailing interface.