Understanding and overcoming the bottlenecks that limit carrier mobility in wide-band-gap III-nitrides is essential for advancing high-performance electronic and optoelectronic technologies. Here we employ state-of-the-art ab initio Boltzmann transport calculations, incorporating fully resolved electron-phonon interactions, to evaluate the carrier mobilities of GaN and AlN in their wurtzite, hexagonal, and haeckelite (4|8) phases. We identify a robust mobility ordering of haeckelite > wurtzite > hexagonal for both electrons and holes, with mobility enhancements exceeding 50–250% in the haeckelite phases. By analyzing mode- and energy-resolved scattering spectra, we demonstrate that this improvement originates from a symmetry-driven suppression of piezoelectric acoustic scattering when the noncentrosymmetric wurtzite lattice transforms into the centrosymmetric haeckelite structure. In the absence of piezoelectric coupling, acoustic scattering reduces to deformation-potential behavior, while optical scattering becomes the dominant channel. The resulting decrease in low-energy scattering rates produces markedly enhanced mobilities, particularly for holes, where traditional III-nitride materials have long faced intrinsic limitations. Our findings reveal phase engineering as an effective route to mitigating phonon-limited transport in III-nitrides and suggest haeckelite structures as promising candidates for next-generation high-mobility electronic and quantum devices.

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• Carrier dynamics
• Crystal structure
• Crystal symmetry
• Electronic structure
• Phonons
• Piezoelectricity
• Wide band gap systems
• Boltzmann theory