**1. Introduction**

Silicon carbide (SiC) is predestined for the fabrication of high power, high temperature and high frequency semiconductor devices, due to its outstanding properties. Despite the commercial availability of SiC power devices, like vertical MOSFETs or Schottky barrier diodes, some topics are not fully understood yet and need further investigations. One major topic is the understanding of ohmic contact formation mechanism on p-doped 4H-SiC [1], due to its importance in the fabrication of bipolar power devices, like pin-diodes or Insulated Gate Bipolar Transistors (IGBTs).

In order to fabricate reliable and low ohmic contacts on p-doped 4H-SiC, various metals and metal stacks have been investigated [1,2]. Due to rather low obtained contact resistivities Ti/Al based metal stacks have become a quasi-standard for ohmic contacts on p-type SiC [1–3]. Numerous studies with different Ti/Al ratios and stacking sequences as well as varying Al surface concentrations fabricated by epitaxial growth or implantation were done in order to fabricate low-ohmic contacts on p-doped 4H SiC [3–11]. These studies have shown the possibility of fabricating ohmic contacts with a specific contact resistance *ρ<sup>C</sup>* down to 10−<sup>6</sup> Ωcm<sup>2</sup> [2,6].

It was also shown that the formation of Ti/Al based low ohmic contacts correlates with the appearance of Ti3SiC<sup>2</sup> on the 4H-SiC surface. Several investigations in literature have revealed an epitaxial growth of Ti3SiC<sup>2</sup> during contact formation [3,8,11–16]. Maeda et al. have described that the epitaxial growth of Ti3SiC<sup>2</sup> consists of two separate reactions (see Equations (1) and (2)) [14].

$$Ti + 3Al = TiAl\_3 \text{ at } 959 \text{ K} \tag{1}$$

$$2\text{SiC} + 3\text{TiAl}\_3 = \text{Ti}\_3\text{SiC}\_2 + 9\text{Al} + \text{Si at } 1270\text{ K} \tag{2}$$

Ti3SiC<sup>2</sup> formation is key for ohmic contact formation mechanism [1–3,6,8,12,17]. Notwithstanding these results, the formation mechanism of Ti/Al based ohmic contacts on

p-doped 4H-SiC is not fully understood [1]. Therefore, this work investigates the underlying formation mechanism and sets up a theory for the contact formation mechanism by analyzing and simulating the Ti/Al based ohmic contacts interface.
