Metastable Ge 1Ϫy C y alloys were grown by molecular beam epitaxy as homogeneous solid solutions having a diamond lattice structure. The substrates were ͑100͒ oriented Si wafers and the growth temperature was 600°C. We report on measurements of the composition, structure, lattice constant, and optical absorption of the alloy layers. In thick relaxed layers, C atomic fractions up to 0.03 were obtained with a corresponding band gap of 0.875 eV. These alloys offer new opportunities for fundamental studies, and for the development of silicon-based heterostructure devices.

Si1−x−yGexCy films ( x≊0.90, y⩽0.02) were grown by molecular beam epitaxy on Si substrates. Infrared optical absorption was used to obtain the band gap energy at room temperature. Biaxial strain obtained from x-ray diffraction measurements verified the presence of nearly relaxed films, and the total and substitutional C contents were obtained from channeling C-resonance backscattering spectrometry. We show by direct measurements that interstitial C had a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1−xGex alloys. While strain decreases the band gap, the effect of substitutional C on the band gap depends on the Si and Ge fractions.

In this letter, we report on heterostructure bipolar transistors ͑HBTs͒ based on silicon carbide ͑SiC͒ and a silicon carbide:germanium ͑SiC:Ge͒ alloy. The SiC:Ge base alloy was formed by the ion implantation of Ge into p-type 4H-SiC and subsequent annealing. HBT mesa structures were fabricated using a reactive ion etching process. The incorporation of Ge was found to increase the gain and the Early voltage of the devices. A common-emitter current gain ͑␤͒ of greater than 3 was measured for the SiC:Ge HBTs. Homojunction SiC transistors were fabricated as a reference using the same process ͑except no Ge in the base region͒ and exhibited a ␤ of 2.2. The transistors exhibited high breakdown voltages ͑Ͼ50 V without passivation͒, that typify SiC-based devices. These results indicate that SiC:Ge is a promising material for use in SiC-based heterostructure devices.

No abstract

No abstract