Fabrication and Characterization of Structures and Rectifiers Based on Silicon Carbide Alloyed with Germanium PDF Download

Author: Gary L. Katulka
Publisher:
ISBN: 9780549393603
Category : Germanium alloys
Languages : en
Pages :

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Book Description
SiC possesses highly unique and interesting properties. The large bandgap and extremely high thermal conductivity make it an excellent material candidate for high voltage and high power electronics which can be exploited for both commercial and military applications. The chemical inertness of SiC is advantageous for applications requiring tolerance to harsh environments and very high temperatures, owing mainly to the strong Si-C sp3 bond. While fabricating ohmic contacts for SiC is very challenging due to large surface barrier heights, once formed the contacts are thermally stable to extremely high temperatures. We have shown in our experiments that specialized ohmic contacts on 4H-SiC are stable and exhibit resistivity changes of at most 3.8% for contacts exposed to the temperature range of 600-1120°C and current densities of 2.5 kA/cm 2 . Reported for the first time by our group in 1999 at the University of Delaware, heterostructure devices with newly developed SiC:Ge alloys were extensively investigated. Rutherford Backscattering Spectrometry (RBS) and X-ray diffraction (XRD) measurements demonstrated thermal stability of the material up to 1000°C and implied an increase in the lattice constant. Although the only practical method for impurity doping, due to the very low diffusivity in SiC, is with ion implantation we experimentally measured the diffusivity of Ge in SiC in the range of 1.05 x 10 -15 cm 2 /s to 1.45 x 10 -15 cm 2 /s. This is considered valuable new information for purposes of precise device processing, considering the implant and contact anneal temperatures for SiC are in excess of 1000°C. SiC/SiC:Ge rectifiers were fabricated and analyzed in collaboration with Northrop Grumman, Baltimore, MD. Our experimental measurements from the rectifiers revealed the forward current was higher by as much as 0.5 mA for SiC/SiC:Ge devices compared to devices without Ge, and built-in voltages were consistently lower by between 100-42 mV. Contact resistance studies showed that SiC:Ge rectifiers had a greatly reduced contact resistance and specific contact resistivity compared to un-implanted SiC devices, for both n and p conductivity types. The Ge in n-SiC reduced the contact resistance and the specific contact resistivity by a factor of 5.6 and 8.8, respectively. In p-SiC, the Ge had an even more pronounced effect, reducing the contact resistance by a factor of 18.6 and lowering the specific contact resistivity by a factor of 14.5. Finally our 2MeV He+ RBS channeling studies suggested that a significant portion of the Ge in SiC:Ge implanted substrates was physically located on Si substitutional lattice sites within the host 4H-SiC crystal. This was true for samples containing between 0.6% and 1.25% Ge, and numerous channeling angles were utilized in the study with support from the Ion Beam Lab at the University of Michigan, Ann Arbor, MI. These results are considered highly important experimental findings which corroborate our earlier work and further promote SiC:Ge as a viable semiconductor material for high-power, high-temperature heterostructures with 4H-SiC.