Free-carrier mobility in GaN in the presence of dislocation walls - art. no. 115202

The free-carrier mobility versus carrier density in n-type GaN grown by low -pressure metal-organic vapor-phase epitaxy on a sapphire substrate experie nces a particular behavior that consists of the appearance of a sharp trans ition separating a low- from a high-mobility regime. This separation appear s as soon as the carrier density exceeds a critical value that depends on t he growth process. Using low-field electrical transport simulations, we sho w that this particular mobility behavior cannot be simply interpreted in te rms of dislocation scattering or trapping mechanisms, but that it is also c ontrolled by the collective effect of dislocation walls (the columnar struc ture). As the free-carrier density increases, the more efficient screening properties result in the transition from a barrier-controlled mobility regi me to a pure-diffusion-process-controlled mobility regime. The model permit s us to reproduce the experimental mobility collapse quantitatively.