Germanium Carbon alloys are a potentially very interesting class of new electronic and perhaps electro-optic materials about which little is known. A remarkable feature of the materials is that they remain near direct gap materials, at least for a few % C incorporation. A 1.1 eV bandgap material has already been made using reactive plasma deposition, and it shows much higher absorption than c-Si with the same bandgap.
In order to incorporate more C into Ge, and to incorporate more Ge into SiC, the group at the University of Nebraska-Lincoln (UNL) has developed a novel, low temperature, deposition technique (hollow cathode plasma jet deposition) to provide sputtered Ge, sputtered C, sputtered Si and a highly reactive H beam. Each material can be independently controlled, and therefore, much greater amounts of C can be incorporated than is possible using a standard reactive plasma ECR or a glow discharge reactor. We have already shown that this technique is capable of producing high quality a-(Si,Ge) films, and now we want to explore the use of this technique to produce well controlled, crystalline films of Ge 1-xCx . Both microcrystalline films on glass, and crystalline films on Ge or Si substrates will be explored. A systematic set of material properties, including structural, optical and electronic properties, will be measured at UNL and Iowa State University (ISU). The structural measurements include x-ray diffraction, Raman spectroscopy, SEM and TEM, constant photo-electron spectroscopy and FTIR to measure H bonding in the material. Optical measurements will include measurement of n and k using ellipsometry, spectro- photometry and double-beam photo-conductivity techniques. Electronic measurements will include mobility measurements, type of doping, dopant levels, mid-level defects using DLTS, the type of recombination, etc. Given the importance of the materials to devices, proof of concept p-n junctions will be made. The deposition system can introduce dopants such as B and P during growth. Electronic properties such as minority carrier lifetime and diffusion lengths will be measured in devices. This will be the first systematic exploration of this novel material system. Virtually nothing is known about the fundamental device-related properties of this system.
II. Broad Impact The potential industrial impact has already been described above. We plan a very activeinvolvement of both undergraduate and graduate students in the program. There will be exchanges of graduate and undergraduate students between UNL and ISU. Both institutions teach courses in semiconductor materials and devices, including lab courses. ISU plans to offer a new, advanced semiconductor material fabrication and characterization course, and the results from this project will be integrated into that new course.
