The characteristics of p-type Mg-doped GaN films diffused with Si are studied. N-type conductivity is achieved, and the carrier mobility of diffused GaN is 90-150 cm(2)V(-1) s(-1), higher than that of p-GaN but less than that of epitaxially grown n-GaN. The Mg acceptor states could become deep compensating defects, and the compensation ratio N-A/N-D is 0.3, 0.45, 0.6, and 0.75 for 800, 900, 1000, and 1100 degreesC diffused GaN, respectively. The carrier transport may be dominated by electron hopping through these deep compensating centers or through diffusion. The results of temperature-dependent carrier concentration indicate that thermal annealing may induce defects at the surface, leading to an additional activation energy E(d)similar to10 meV in the 200-500 K region in diffused GaN. (C) 2004 American Vacuum Society.