Basic Principles of Ohmic Contacts for N-type SiC and P-type SiC?

The fundamental principle of ohmic contact for N-type silicon carbide (SiC) and P-type SiC is to establish an electrical connection with minimal contact resistance through suitable electron transfer between the metal material and the SiC material.

• For N-type SiC, its conductivity is primarily contributed by additional free electrons. When a metal contacts N-type SiC, free electrons from the metal can easily enter the N-type SiC, forming electron injection. This results in a low-resistance contact in the SiC.

• For P-type SiC, its conductivity is mainly contributed by holes. When a metal contacts P-type SiC, free electrons from the metal combine with holes in the P-type SiC, forming electron-hole pairs and reducing the hole concentration. This enables the formation of a low-resistance contact.
• The fundamental principle of ohmic contact for N-type and P-type SiC involves establishing low-resistance contacts through electron transfer between the metal and the SiC.

Aluminum (Al)-based metals are considered effective acceptor elements in SiC for the following reasons:

     1. High Free Defect Concentration: In SiC materials, aluminum atoms can induce a high concentration of free defects. This is because aluminum atoms can form additional localized defects in the SiC lattice, such as aluminum vacancies and localized impurity energy levels. These defects and energy levels provide additional energy states, influencing processes such as charge carrier diffusion and recombination, thereby affecting the electrical properties of the material.

     2. Doping Effect: Aluminum doping can change the electron concentration type of SiC, transforming it from N-type (conductivity contributed by free electrons) to P-type (conductivity contributed by holes). This doping effect gives aluminum significant application value in SiC, such as in the fabrication of bipolar power devices.

     In summary, aluminum is an effective acceptor element in SiC because it can introduce a high concentration of free defects and alter the electron concentration type of the material, thereby significantly impacting the electrical properties of SiC materials.