  Rocksalt ScN is a semiconductor with a small lattice mismatch to wurtzite
GaN. Within the modern theory of polarization, ScN has a nonvanishing formal
polarization along the [111] direction. As a result, we demonstrate that an
interface between (0001) GaN and (111) ScN exihibts a large polarization
discontinuity of $-$1.358 $\rm Cm^{-2}$. Interfaces between ScN and wurtzite
III-nitrides will exhibit a high-density electron gas on the (000$\bar{1}$) GaN
interface or a hole gas on the (0001) GaN interface, with carrier
concentrations up to $8.5 \times 10^{14}$ cm$^{-2}$. The large polarization
difference and small strain makes ScN a desirable choice for
polarization-enhanced tunnel junctions within the III-nitride materials system.
The large sheet carrier densities may also be useful for contacts or current
spreading layers.
