Optical properties of Ge 1-y C y alloys

The Ge1-yCy semiconductor alloy system offers promise as a material for use in heterostructure devices based on Si as well as other materials. We have grown Ge1-y Cy alloys by solid source molecular beam epitaxy on Si substrates. Layer thicknesses ranged from 0.01 to 3 µm, and Auger electron spectroscopy and secondary ion mass spectrometry indicated C fractions up to 3 at. %. Optical absorption in the near-infrared region indicated a shift in the energy bandgap from that of Ge which was attributed to the effects of alloying. The dependence of the bandgap on composition was consistent with linear interpolations of the Ge and C conduction band minimums. We observed a fundamental absorption edge characteristic of an indirect bandgap material. Photoluminescence spectra at 11K of thick, relaxed layers indicated single broad peaks near the expected bandgap energy.