Carbon structural transitions and ohmic contacts on 4H-SiC

Abstract

The structural properties of sputtered carbon films on SiC are investigated using X-ray photoelectron spectroscopy (XPS) and Raman scattering. The asdeposited films are amorphous with an sp 2 /sp 3 ratio of 1. The sp 2 carbon structures gradually increase with increasing temperatures and consist of amorphous aromatic-like carbon, polyene-like carbon, and nano-size graphite flakes. Schottky contacts on carbon/SiC are converted to ohmic contacts after annealing. The concentration of nano-graphitic flakes relative to the aromatic-like and polyene-like carbon increases nearly linearly with annealing temperature. Stacked graphitic structures are not observed. The specific contact resistivities are at 10 Ϫ3 -10 Ϫ4 ⍀cm 2 on the carbon/SiC after annealing from 1050°C to 1350°C.

Microstructure evolution and diffusion of ruthenium in silicon carbide, and the implications for structural integrity of SiC layer in TRISO coated fuel particles

“…The reaction zone is observed to grow with increasing annealing temperature. The Ru/4H-SiC interface of the as-deposited sample as depicted in Fig [ 6,7,8,9,10,11] . The intensity ratio of the D and G peaks can be used to approximate the size of the crystalline graphite or degree of disorder of the graphite that is formed [6].…”

Solid State Reaction of Ruthenium with 6H-SiC Under Vacuum Annealing and the Impact on the Electrical Performance of its Schottky Contact for High Temperature Operating SiC-Based Diodes

“…Ru is observed to react with 6H-SiC, and is found at 2300 x 10 15 at./cm 2 from the surface (Fig.6) after annealing at 1000 o C. Raman analysis of the thin film sample (Fig. 7) shows the formation of graphite as indicated by a typical carbon D peak at 1354 cm -1 and G peak at 1589 cm -1 [12,13,14,15,16,17] . The intensity ratio of the D and G peak are used to approximate the size of the crystalline graphite or degree of disorder of the graphite .…”

“…This finding is supported by Seyller et al [30] who in their studies found that the formation of graphite at the metal-SiC interface may lead to ohmic contact formation as the SBH of graphite on n-type 6H-SiC is very small (about 0.3 eV) . Lu et al [13] also found out that the carbon contact on SiC exhibited schottky and ohmic contact behaviour in the annealing temperature range of 900-1350 o C. They found that the temperature of transition from schottky to ohmic contact in Carbon/SiC structure depends on the doping concentration of SiC and amount of nano-graphitic flakes formed. *CV curve is not a straight line.…”

“…The D band is generally thought to be an indication of disordered or defective hexagonal planar graphite structures [12]. The G band originates from the stretching vibrations in the basal plane of ideal graphite, and a combination of D and G bands is generally regarded as an indication of polycrystalline graphitic structures [13]. According to Lu et al [13] the absence of a broad amorphous carbon peak at position 1510 cm -1 in the Raman spectrum is an indication of the absence of this type of carbon in the sample.…”

“…The G band originates from the stretching vibrations in the basal plane of ideal graphite, and a combination of D and G bands is generally regarded as an indication of polycrystalline graphitic structures [13]. According to Lu et al [13] the absence of a broad amorphous carbon peak at position 1510 cm -1 in the Raman spectrum is an indication of the absence of this type of carbon in the sample. There is also an indication from Raman analysis of the formation of Ru 2 Si 3 as evidenced by the appearance of the peak immediately left of 300 cm -1 position [18].…”