Morphological transition of Si1-xGex films growing on Si(100).: II.: Synchrotron-radiation-excited chemical-vapor deposition:: From two-dimensional growth to growth in the Volmer-Weber mode

The morphological evolution of Si1-xGex films growing under conditions of excitation by high-energy photons (hv>100eV) has been investigated by means of in situ spectroscopic ellipsometry. An atomically discontinuous wetting layer is produced by the incidence of the products of photolysis from Si2H6 and GeH4 on a hydrogen-terminated Si(100) surface. At temperatures of growth below 300 degreesC, a uniform Si1-xGex layer grows because of the strong hydrogen surfactant effect and the low mobility of the Si and Ge adatoms. At temperatures above 400 degreesC, most of the Si adatoms are in the form of monohydride and Ge adatoms are free of bonds with hydrogen atoms. On a partially hydrogen-covered surface, the number of dangling-bond terminated nucleation centers is restricted, while the migration of the adatoms is enhanced. This results in islanding with roughness up to a maximum height of about 100 A from the initial stages of growth. Since the grain boundaries between islands become the sources of dislocations, the strain stored in the Si1-xGex islands is completely relieved. This leads to early coalescence so that a flat overlayer surface is recovered. (C) 2002 American Vacuum Society.