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Defects and Impurities in 4H- and 6H-SiC Homoepitaxial Layers: Identification, Origin, Effect on Properties of Ohmic Contacts and Insulating Layers and Reduction.

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Quarterly technical rept. 17 Jul-30 Sep 95,

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The design and construction of a new and unique CVD system for the deposition and analysis of SiC thin films is underway. Initial measurements of the impact ionization coefficients of electrons and holes in SiC devices have been made. Degradation in breakdown voltage and an increase in the leakage current were observed. Analytical expressions were derived for the extraction of impact ionization coefficients from I-V data. Simulations were performed for a simple p-n junction diode, with and without impact ionization, and impact ionization coefficients were extracted using the analytical expressions derived. NiAl contacts with Ni passivating layers were deposited at room temperature on p-type 6H-SiC 0001 substrates. As-deposited contacts were rectifying with very low leakage current densities approx. 1 x 10 exp -8 Asq cm at 10 V, ideality factors between 1.4 and 2.4, and a Schottky barrier height SBH of approximately 1.37eV. The contacts on p 1 x 10exp cm were ohmic after annealing for 10-80 s at 1000 deg C in a N2 ambient. The estimated specific contact resistivity from a non-mesa etched TLM pattern was 2-3 x 10exp- 2 ohms sq cm. The NiNiAl contacts deposited on SiC with lower carrier concentrations 1-5 x 10 exp 18 cu cm were not ohmic after annealing at 1000 deg C for 10-60 s but became nearly ohmic after annealing for 80 s. As-deposited Ni and Au contacts on p-type 6H-SiC displayed similar current-voltage characteristics with calculated SBHs of 1.31 and 1.27eV, respectively. jg p.2

Subject Categories:

  • Inorganic Chemistry
  • Electrical and Electronic Equipment
  • Electrooptical and Optoelectronic Devices
  • Electricity and Magnetism

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