Application of x-ray diffraction techniques to the structural study of silicon based heterostructures

Abstract

X-ray techniques have been applied to the characterization of various device type Si–Ge heterostructures. Double crystal diffractometry was used to evaluate the crystal perfection and thermal stability of buried Si1−xGex layers used in heterojunction bipolar transistors and of Si1−xGex/Si superlattices used in p-i-n photodetectors. The glancing incidence x-ray technique is more sensitive to the near surface region and better suited to study thin layered structures. This method was used to obtain the structural parameters of SimGen short-period superlattices. Ultrathin buried Ge layers (1–12 monolayers) on (100) Si were also investigated by analyzing intensity oscillations in the reflected x rays arising from interference effects. This technique is sensitive enough to detect Ge layers one atomic layer thick. Comparison of the measured and calculated reflected intensity also provided an estimate of the morphology and interface sharpness of these heterostructures. The same technique was also applied to the study of a very thin heavily erbium-doped Si epilayer.