Nonequilibrium effects in the channeling of energetic particles through ultrathin Si/Ge/Si heterostructures: A Monte Carlo study

Noneuilibrium phenomena in the channeling of 1.8-MeV He+ in (2--6)-ML-thick (ML, monolayer) pseudomorphic films of Ge on Si(100) capped with 148 ML of crystalline Si are investigated by use of Monte Carlo techniques. The large asymmetry in the channeling angular scans is related to the strain in the ultrathin film and can be used as a sensitive measure of that strain. The two lattice parameters of interest, at the Si/Ge interface and of the strained Ge film, are extracted by comparing experimental results with simulations. The relevant features in the angular scans on which this determination is based are very sharp functions of angle, typically of 0.250 full width at half maximum. Possible systematic errors arising from this, as well as the influence of other experimental parameters such as beam divergence and the thickness of the Si cap, are assessed