Relaxation Delay of Ge‐Rich Epitaxial SiGe Films on Si(001)
Andreas Salomon, Johannes Aberl, Lada Vukušić, Manuel Hauser, Thomas Fromherz, Moritz Brehm
Abstract
The realization of several future electronic and optoelectronic Si‐based devices is impeded by the limited critical thickness of strained, pseudomorphic, and Ge‐rich Si 1− x Ge x layers grown on Si(001) substrates, i.e., before their relaxation. Herein, atomic force microscopy is used to investigate the surface morphology of about 170 Si 1− x Ge x /Si(001) samples with various Ge compositions ranging from ≈36% to 100% and film thicknesses from ≈1 to ≈16 nm. Furthermore, by defining the quality standards concerning the surface roughness, the relaxation behavior is explored for epitaxial films with x significantly larger than 50%, which is experimentally lacking to date. Thereby, it is found that by lowering the substrate temperature during molecular beam epitaxy growth to 350 °C, Ge‐rich and dislocation‐free epitaxial films with an excellent root‐mean‐square surface roughness of <0.2 nm can be deposited. Furthermore, the low surface roughness is conserved for thicknesses well beyond the theoretical predictions of People and Bean.