  N-polar GaN channel mobility is important for high frequency device
applications. In this Letter, we report the theoretical calculations on the
surface optical (SO) phonon scattering rate of two-dimensional electron gas
(2-DEG) in N-polar GaN quantum well channels with high-k dielectrics. The
effect of SO phonons on 2-DEG mobility was found to be small at >5 nm channel
thickness. However, the SO mobility in 3 nm N-polar GaN channels with high-k
dielectrics is low and limits the total mobility. The SO scattering for SiNx
dielectric GaN was found to be negligible due to its high SO phonon energy.
