The physics and technology of metal/semiconductor interfaces are key-points in the development of silicon carbide (SiC) based devices. Although in the last decade, the metal to 4H-SiC contacts, either Ohmic or Schottky type, have been extensively investigated with important achievements, these remain even now an intriguing topic since metal contacts are fundamental bricks of all electronic devices. Hence, their comprehension is at the base of the improvement of the performances of simple devices and complex systems. In this context, this paper aims to highlight some relevant aspects related to metal/semiconductor contacts to SiC, both on n-type and p-type, with an emphasis on the role of the barrier and on the carrier transport mechanisms at the interfaces.

Studying the temperature dependence of the electrical properties of Ohmic contacts formed on ion-implanted SiC layers is fundamental to understand and to predict the behaviour of practical devices. This paper reports the electrical characterization, as a function of temperature, of Nibased Ohmic contacts, simultaneously formed on both n-or p-type implanted 4H-SiC. A structural analysis showed the formation of the Ni 2 Si phase after an annealing leading to Ohmic behaviour. The temperature-dependence of the specific contact resistance indicated that a thermionic field emission mechanism (TFE) dominates the current transport for contacts formed on p-type material, while a field emission (FE) is likely occurring in the contacts formed on ntype implanted SiC. The values of the barrier height were 0.75 eV on p-type material and 0.45 eV on n-type material. The thermal stability of the current transport mechanisms and related physical parameters has been demonstrated upon a long-term (up to 95 h) cycling in the temperature range 200-400 °C.

A practical model, adequate for full reproduction of inhomogeneous Schottky diodes' forward characteristics over wide high-temperature and bias ranges, is proposed. According to this p-diode model, the Schottky contact current is considered to flow through m parallel-connected internal diodes, each with stable, constant barrier height and specific series resistance (both main model parameters). The value of m, required to reproduce the entire electrical forward behavior of a non-uniform Schottky contact, is directly connected to a particular model parameter (peff), used to define the inhomogeneity degree. The p-diode model was tested on forward characteristics measured for both Ni and commercial Ti Schottky diodes on 4H-SiC, which exhibited varying degrees of inhomogeneity. Excellent replication of experimental curves was achieved for all investigated samples, even those with obvious irregularities, such as "humps", explained in the model by the series resistances' influence. In the case of m=1, the proposed model does not produce identical results with the conventional model of a homogeneous Schottky contact if peff ≠ 0. The value of this parameter indicates how much of an inhomogeneous contact's area is essentially used for current conduction.

This work reports on the morphological and electrical properties of Nibased back-side Ohmic contacts formed by laser annealing process for SiC power diodes. Nickel films, 100 nm thick, have been sputtered on the back-side of heavily doped 110 µm 4H-SiC thinned substrates after mechanical grinding. Then, to achieve Ohmic behavior, the metal films have been irradiated with an UV excimer laser with a wavelength of 310 nm, an energy density of 4.7 J/cm 2 and pulse duration of 160 ns. The morphological and structural properties of the samples were analyzed by means of different techniques. Nanoscale electrical analyses by conductive Atomic Force Microscopy (C-AFM) allowed correlating the morphology of the annealed metal films with their local electrical properties. Ohmic behavior of the contacts fabricated by laser annealing have been investigated and compared with the standard Rapid Thermal Annealing (RTA) process. Finally, it was integrated in the fabrication of 650V SiC Schottky diodes.

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