In this letter, the uniform 4H silicon carbide (SiC) mesopores was fabricated by pulsed electrochemical etching method. The length of the mesopores is about 19 μm with a diameter of about 19 nm. The introduction of pause time (Toff) is crucial to form the uniform 4H-SiC mesopores. The pore diameter will not change if etching goes with Toff. The hole concentration decreasing at the pore tips during the Toff is the main reason for uniformity.

The Ti electrode was deposited on the (0001) face of an n-type 4H-SiC substrate by magnetron sputtering. The effect of the electrode placement method during the annealing treatment on the contact property was carefully investigated. When the electrode was faced to the Si tray and annealed, it showed ohmic behavior, otherwise it showed a non-ohmic property. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to characterize the electrode phase, composition, thickness, and surface morphology. The additional silicon introduced from the Si tray played a key role in the formation of the ohmic contact on the Ti/4H-SiC contact.

The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρc) is 1.97 × 10−3 Ω·cm2, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC.

Nickle ohmic contacts on the Si-face of n-type 4H-SiC are prepared by both rapid thermal annealing (RTA) and laser spark annealing (LSA). The effects of the different annealing procedures on the cathode surface morphology, cathode/substrate cross sectional morphology, element composition, microscopic structure of carbon clusters in the SiC substrate near surface, are characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), transmission electron microscopy (TEM), and Raman spectra, respectively. The tests and analyses show that both thermal treatments can help to form ohmic contacts. The specific contact resistances of RTA sample and LSA sample are measured to be 5.2× 10-4 Ω ·cm2 and 1.8× 10-4Ω·cm2 by transmission line model, respectively. The Ni film of RTA sample shrinks badly thus forms tiny islands on the surface, while the surface of LSA sample remains relatively smooth. The root-mean-square (RMS) values of surface roughness of the Ni films of as-deposited, RTA and LSA samples are 8.65 nm, 91.3 nm and 17.5 nm, respectively. The Ni/SiC interface of RTA sample corrodes badly, and Si can be found in the whole Ni film, indicating an overall consumption of Ni to react with Si forming NiSi compounds; C atoms, which do not react with Ni atoms，cluster to the average size of about 40 Å, and gather approximately as a layer located about 20-30 nm off the Ni/SiC interface. The Ni/SiC interface of LSA sample is relatively smooth, and a small quantity of Ni atoms diffuse into the SiC wafer, forming lots of ternary phase diffusion zones of about tens of nanometers deep into the SiC wafer, in which C, Si, Ni atoms are distributed uniformly; the average size of C clusters is smaller than that in RTA sample and no obvious C enriched zone was found, while neither Si atom nor C atom is found to diffuse into the Ni film.#br#The ohmic contacts prepared by LSA have obvious advantages compared with those by RTA in many aspects such as cathode surface morphology, interface morphology, uniformity of components in cathode films, etc. All the results mentioned above make LSA a promising method of thermal treatment in preparation of ohmic contacts.