INCORPORATION AND STABILITY OF CARBON DURING LOW-TEMPERATURE EPITAXIAL-GROWTH OF GE1-XCX (X-LESS-THAN-0.1) ALLOYS ON SI(100) - MICROSTRUCTURAL AND RAMAN STUDIES

Low-temperature (-200 degrees C) molecular beam epitaxy of Ge1-xCx all oys grown on Si(100) have been extensively investigated by in situ ref lection high-energy electron diffraction, ex situ x-ray diffraction, t ransmission electron microscopy, and Raman spectroscopy. Carbon concen trations were nominally varied from 0 up to similar to 10 at. %. Selec ted samples were annealed in an Ar ambient at 750 degrees C to evaluat e the stability of the thin films. A few films were also grown on Ge s ubstrates. With increasing C concentration, the epitaxial growth mode changes from two dimensional layer growth to three dimensional island growth. The surface has a tendency to facet along {311} planes under c ertain growth conditions, The microstructure shows an increase in plan ar defect density with increasing C concentration. The x-ray diffracti on data show that the lattice parameter decreases with increasing C co ncentration and that a maximum of 1 at. % C is incorporated substituti onally in Ge, Raman spectroscopy shows no clear Ge-C signal though ext ra intensity is measured at the energies where Ge-C modes may be expec ted. Films with nominal C concentrations greater than 2 to 3 at. % sho w clear evidence for amorphous C. We propose that under our growth con ditions, nominal C in excess of about 2 to 3 at. % remains on the surf ace as amorphous C and plays an important role in 3D islanding, defect formation, and {311} faceting during epitaxial growth. (C) 1997 Ameri can Institute of Physics.