THE GE-C LOCAL MODE IN EPITAXIAL GEC AND GE-RICH GESIC ALLOYS

The Raman signature of the local Ce-C mode for substitutional C is ide ntified as a narrow line (8 cm(-1) full width at half maximum) near 53 0 cm(-1) in alloy films of Ge1-yCy (0 less than or equal to y less tha n or equal to 0.07) grown on Ge (100) substrates by low-temperature (2 00 degrees C) molecular beam epitaxy. The intensity of the Ge-C line r elative to the c-Ge line suggests that only a small fraction of the no minal C is in substitutional sites. In ternary alloys of Ge1-x-ySixCy with x= 0.1 and 0.2 and y = 0.03, the Ge-C mode disappears, suggesting a strong bias towards C bonding with Si as opposed to Ge. In Ge,,Sn, films the Ge-Sn mode is seen at 263 cm(-1). (C) 1998 American Institut e of Physics.