Relaxation Delay of Ge-Rich Epitaxial SiGe Films on Si(001)

The realization of several future electronic and optoelectronic Si-based devices is impeded by the limited critical thickness of strained, pseudomorphic, and Ge-rich Si1-xGex 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 Si1-xGex/Si(001) samples with various Ge compositions ranging from approximate to 36% to 100% and film thicknesses from approximate to 1 to approximate 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 degrees 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.