  Selection rules are presented for electron-phonon scattering in GaN with the
wurtzite crystal structure. The results are obtained for the interband
scattering between the lowest conduction band ($\Gamma$-valley) and the second
conduction band ($U$-valley). These selection rules are derived based on the
original group-theoretical analysis of the crystal vibrations in GaN, which
included detailed compatibility relations for all phonon modes.
