Theoretical simulation of free carrier mobility collapse in GaN in terms of dislocation walls

Using low field electrical transport simulations, we show that the particular mobility behaviour versus carrier density in MOVPE GaN materials, characterized by a mobility collapse at low dopant densities, cannot be simply interpreted in terms of dislocation scattering or trapping mechanisms, but that it is also controlled by the collective effect of dislocation walls (the columnar structure). As the free carrier density increases, the more efficient screening properties result in the transition between a barrier-controlled mobility regime and a pure-diffusion-process-controlled mobility regime. The model permits us to quantitatively reproduce the experimental mobility collapse.