Experimental results show that the room-temperature carrier mobility in bulk layers of undoped or Si-doped GaN grown by LP-MOVPE on sapphire substrate shows a sudden increase as soon as the carrier density exceeds a critical value of about 1018cm-3. We show that such a behavior can be theoretically reproduced by assuming that the columnar structure (i.e. the dislocation microstructure) is responsible for internal electronic barriers.
Farvacque, J. L., Bougrioua, Z., Moerman, I., Van Tendeloo, G., & Lebedev, O. (1999). Role of the defect microstructure on the electrical transport properties in undoped and Si-doped GaN grown by LP-MOVPE. Physica B: Condensed Matter, 273–274, 140–143. https://doi.org/10.1016/S0921-4526(99)00431-7