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In this paper, Pt/TaSi 2 /Ni/Ti/Ni/SiC and Pt/Ti/SiC simultaneous ohmic contacts to n-type and p-type 4H-SiC are studied. The thermal stability and electrical characteristics of the ohmic contacts are investigated and compared after being aged at 500 °C for 300 h in air. The n- and p-type Pt/Ti/SiC ohmic contact failed after 100 h and after 200 h, respectively. While the Pt/TaSi 2 /Ni/Ti/Ni/SiC samples exhibits a good thermal stability and high temperature electrical characteristics, with a relatively small increase of the specific contact resistance (SCR) in the initial 50 h and then remains stable in the rest of the thermal aging duration. SEM analysis reveals that the surface morphologies of Pt/TaSi 2 /Ni/Ti/Ni/SiC samples keep smooth and stable during the aging process. According to AES analysis, the main reason of electrical characteristics degradation is the oxidation on the metal/4H-SiC interface during the aging process. Also, at the expense of the TaSi 2 layer oxidization, the diffusion rate of oxygen atoms towards the SiC are slowed down, and therefore, the metal/4H-SiC interface quality was not affected by oxidation problems and extending the life of ohmic contact in air at 500 °C. Experimental results indicate that the Pt/TaSi 2 /Ni/Ti/Ni/SiC simultaneous ohmic contacts to both n- and p-type SiC are promising to be used for high temperature and harsh environment SiC-based devices. [ABSTRACT FROM AUTHOR]

The properties of 4H–SiC/Ni/Ti/Al/W metal contacts on n-type and p-type ion-implanted 4H–SiC layers are studied in this paper, with the aim of realizing simultaneous ohmic contact formation. The thickness of the Al film and the alloying temperature are analyzed. Specific contact resistances of 8 × 10−4 Ω cm2 and 4.1 × 10−5 Ω cm2 were achieved with multi-metal layer Ni/Ti/Al/W (80/30/110/50 nm) for n-type and p-type 4H–SiC, respectively, at an annealing temperature of 750 °C. This is for first time at such a low annealing temperature that ohmic contacts have been reported to simultaneously form on n-type and p-type 4H–SiC with satisfactory specific contact resistances. Samples were characterized using AFM, XRD, AES and TEM, and the results indicate that the presence of the W top layer facilitates lowering the surface roughness and accumulating elemental Ni and Al on the SiC side during annealing, which benefits the formation of the ohmic contacts. • Ni/Ti/Al/W on n-type and p-type 4H–SiC with various Al layer thicknesses are studied. • Ohmic contacts have been simultaneously formed on n-type and p-type 4H–SiC at 750 °C. • It's for the first time at such a low annealing temperature ohmic contacts have been formed. •The top layer W metal results in the formation of Ni2Si and Al-Rich at the interface. [ABSTRACT FROM AUTHOR]

Abstract: NaAlH4 samples doped with Ce additives, at various stages in a hydrogenation process, are investigated using synchrotron X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) spectroscopy. The presence of Ce–Al alloy regions are detected in the ball-milling samples, and no evidence of changes in the unit-cell dimensions of NaAlH4 are seen between ball-milling and hydrogenation samples. The XANES spectra of the samples are measured at the L-3 edge of the cerium, and by comparing the spectra of the dopants with those of the pure oxides, we find that a valency change of the oxidated states of cerium from Ce4+ to Ce3+. [Copyright &y& Elsevier]