Zeeman splitting of shallow donors in GaN
  The Zeeman splitting of the donor spectra in cubic- and hexagonal-GaN are studied using an effective mass theory approach. Soft-core pseudopotentials were used to describe the chemical shift of the different substitutional dopants. The donor ground states calculated range from 29.5 to 33.7 meV, with typically 1 meV higher binding in the hexagonal phase. Carbon is found to produce the largest donor binding energy. The ionization levels and excited states are in excellent agreement with Hall and optical measurements, and suggest the presence of residual C in recent experiments. 
Francisco Mireles and Sergio E. Ulloa