Schottky diodes on Si1−x−yGexCy alloys: effect of the C-incorporation

Si1−x−yGexCy films have been grown by using a rapid thermal chemical deposition reactor. The growth temperatures were 650°C and 550°C and lead to Ge-contents of about 16% and 10%, respectively. The epilayers were characterized by infrared spectroscopy and Raman spectroscopy. The C-fraction varied from 0 to 1.25%. The shifts of Raman frequencies with increasing C-content cannot be explained in terms of change in strain. Electrical characterizations of tungsten contacts to n- and p-type films were achieved through current-voltage measurements. The Schottky barrier on n-type does not depend on the composition. This result indicates that the Fermi level at the interface with W is pinned relative to the conduction band. The Schottky barrier on p-type increased with the C-fraction. The increased magnitude seems to be too large to be explained in terms of variation of the band-gap-energy. The barrier height, for a given C-fraction, is larger for the films prepared at 550°C. This result can be ascribed to the lower Ge-incorporation at low temperature. Some samples were annealed at 1000°C. As expected, substitutional C-atoms precipitate to form silicon carbide. This formation of β-SiC precipitates results in detrimental effects on Schottky diode properties.