In situ RHEED monitoring of carbon incorporation during SiGeC/Si(001) growth in a UHV-CVD system

In situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM) and high resolution X-ray diffraction (XRD) have been combined to investigate the kinetics of carbon incorporation during the growth of SiGeC alloys on Si(001) in an ultrahigh-vacuum chemical-vapor deposition system. At a given growth condition of substrate temperature and total growth pressure, three distinct growth regimes can be identified from RHEED as a function of the methylsilane partial pressure. At low methylsilane partial pressures, a two-dimensional growth RHEED pattern is observed and TEM investigations indicate that the grown films are defect-free up to a thickness of at least three times larger than the critical thickness without carbon. When the methylsilane partial pressure exceeds a threshold value, a transition from two-dimensional growth to islanding growth is detected from RHEED. At the same time, the substitutional carbon content—as determined by XRD rocking curves—is found to decrease. For high methylsilane partial pressures, RHEED patterns reveal the appearance of extra diffraction spots, which can be attributed to the formation of stacking faults and/or twins along the [111] planes. Since the growth mode transition during SiGeC growth is found to occur only after the deposition of a certain thickness—whose value depends on the methylsilane flow—we propose a concept of multilayer-array growth, following which defect-free SiGeC films with substitutional carbon contents higher than 3% can be achieved.