It was recalled that the free-carrier mobility versus carrier density in n-type samples, grown via low-pressure metal-organic vapour-phase epitaxy onto a sapphire substrate, exhibited a behavior which involved the appearance of a sharp transition that separated a low-mobility regime from a high-mobility regime. This separation appeared as soon as the carrier density exceeded a critical value that depended upon the growth process. By using low-field electrical transport simulations, it was shown that this mobility behavior could not be interpreted simply in terms of dislocation-scattering or trapping mechanisms. It was also controlled by the collective effect of dislocation walls (columnar structure). As the free-carrier density increased, the more efficient screening properties resulted in a transition from a barrier-controlled mobility regime to a purely diffusion-controlled mobility regime. The model quantitatively reproduced the observed mobility collapse.

Free-Carrier Mobility in GaN in the Presence of Dislocation Walls. J.L.Farvacque, Z.Bougrioua, I.Moerman: Physical Review B, 2001, 63[11], 115202 (8pp)