Kohn-Luttinger Interference Effect and Location of the Conduction-Band Minima in6H SiC

Recent Raman-scattering results place the conduction-band minima of $6H \mathrm{SiC}$ on the $M-L$ symmetry line, leaving undetermined the parameter $k_z$ that is required to fix their positions exactly. This parameter could be established by electron-nuclear-double-resonance (ENDOR) measurements, as a similar parameter is for Si, but the present ENDOR results for $6H \mathrm{SiC}$ are insufficient. The Raman result determines the planar part of the donor Kohn-Luttinger interference pattern, and it is found that the highly symmetric pattern concentrates the donor-electron density on lattice sites of planes like the donor plane. Because of the Bloch portion of the wave function, this leads to binding-energy differences for the three inequivalent nitrogen donors, for each donor has a distinct set of neighboring like planes. Whether or not a like plane is favorably placed for a binding-energy enhancement depends on the axial interference factor, which is a function of $k_z$. Thus, an interpretation of the donor binding energies is used to determine $k_z$. The suggested $k_z$ is one for which $6H \mathrm{SiC}$ has six conduction-band minima.