CONTROL OF COMPOSITION AND CRYSTALLINITY IN THE MOLECULAR-BEAM EPITAXY OF STRAIN-COMPENSATED SI1-X-YGEXCY ALLOYS ON SI

In this paper, we present a mass-spectrometry-based approach to the co ntrol of C concentration during molecular beam epitaxy (MBE) of Si1-x- yGexCy/Si superlattices. High-resolution X-ray diffraction, ion beam a nalysis, and transmission electron microscopy (TEM) were used to chara cterize composition and crystallinity in a series of superlattices for which the average strain condition was designed to range from biaxial compression to biaxial tension. For each sample, secondary ion mass s pectrometry and Rutherford backscattering spectrometry confirmed that the average composition of each Si1-x-yGexCy layer was constant during growth. However, TEM revealed strain contrast variations within the S i1-x-yGexCy layers, leading to the conclusion that the presence of C o n the wafer surface leads to laterally inhomogenous incorporation of C (and possibly Ge). TEM also showed that all samples were essentially free of extended defects except for short microtwins observed in the t ensile-strained sample, that originated in the Si1-x-yGexCy lavers and terminated in the Si lavers directly above.