Materials characterization of Si 1− x− yGe xC y/Si superlattice structures

Abstract

Pseudomorphic Si 1− x− y Ge x C y /Si superlattice structures on Si were prepared by molecular beam epitaxy in the compositional range: 8< x<44% and 0< y<4.4%, with layer thicknesses between 5 and 35 nm. Comprehensive materials characterization was carried out by Rutherford and C-resonance backscattering combined with ion channeling. Complementary analysis was provided by secondary ion mass spectrometry (SIMS) and high-resolution transmission electron microscopy. The Si 1− x− y Ge x C y layer composition was derived by measuring the average Ge and C concentrations by ion backscattering and the layer thicknesses from electron micrographs. Carbon depth profiles of good sensitivity were derived from SIMS profiling. The superlattice strain was measured by X-ray diffraction and usually found to be compressive. However, lattice-matched and tensile superlattice films were obtained for alloys with ∼10% Ge. The tensile film had growth defects — microtwins and stacking faults — which could be observed by TEM and detected by ion channeling.