Fundamentals of Silicon Carbide Technology: Growth, Characterization, Devices and Applications

Appendix A

Incomplete Dopant Ionization in 4H-SiC

Dopants atoms in silicon carbide are incorporated substitutionally in place of either a silicon or carbon atom in the hexagonal crystal lattice. Due to the stacking sequence of the polytype, not all silicon or carbon sites are equivalent in terms of their surroundings, and each donor or acceptor can exhibit multiple site-dependent energy levels. Dopants on cubic sites typically have higher ionization energies than dopants on hexagonal sites.

Aluminum is the principal p-type dopant in 4H-SiC, and occupies either a hexagonal or a cubic silicon site, having ionization energies of 197.9 and 201.3 meV respectively [1]. The primary n-type dopants are nitrogen and phosphorus. Nitrogen substitutes for carbon, and on a hexagonal C-site it has an ionization energy of 61.4 meV. Phosphorus substitutes for silicon, and on a cubic Si-site it has an ionization energy of 60.7 meV [1].

Because of its high ionization energy, aluminum acceptors in neutral regions of 4H-SiC are not fully ionized at room temperature. The density of ionized acceptors (and donors) is denoted by (and ), respectively. Incomplete ionization has a profound effect on device performance, and must be taken into consideration in our equations. Nitrogen and phosphorus donors ...