X-ray photoelectron diffraction investigation of Ge segregation and film morphology during first stage heteroepitaxy of Si on Ge(001)

Abstract

X-ray photoelectron diffraction (XPD) and its chemical selectivity have been used in conjunction with surface atom titration by ultra-violet photoelectron spectroscopy and conventional X-ray photoelectron spectroscopy to investigate the interplay between Ge segregation and growth morphology in the earliest stages (0–12 monolayers) of Si solid-source-epitaxy on Ge(001)-2 × 1 surfaces held at room temperature (RT) and at 400°C. A detailed examination, as a function of the Si coverage, of the forward scattering peak contrasts in the [111] and [001] directions of the Si 2p and Ge 3d polar angle distributions provides a diagnostic of whether or not a particular atom is in the top layer (segregation) and yields information about the stacking sequences (morphology). These investigations allowed us to conclude in favour of an initial Si bilayer patch-growth-mode exempt of segregation at RT and of a floating Ge surface at 400°C, the Si agglomeration staying rather mild in the first monolayers. Accessorily, the XPD-specific problems of electron defocusing effects through long atomic chains and strain-induced lattice expansion or contraction have also been addressed.