Investigation on the P-type activation mechanism in Mg-doped GaN films grown by metalorganic chemical vapor deposition

An investigation on the p-type activation in Mg-doped GaN epilayers has bee n carl-led out in relation to the defect structure. The samples were grown by the metalorganic chemical vapor deposition method. Sapphire with (0001) orientation (C-face) was used as the substrate. After growth, the samples w ere heat-treated under Bowing N-2, at temperatures ranging from 600 to 850 degrees C. The p-type activation arises from the dissociation of electrical ly inactive Mg-H complexes and the neutralization of the dissociated H+ dur ing the annealing process. The annealing temperature dependence of hole con centration and hole mobility was studied. The p-type activation process res ulted in a different maximum hole concentration and an optimum annealing te mperature. Subsequent microstructural characterization of our samples revea led that the dislocations play a key role in p-type conductivity and may ex plain the difference observed in the electrical properties. Indeed, the ana lyses of transmission electron microscopy (TEM) images and X-ray diffractio n (XRD) data show that Mg-doped GaN exhibits a different X-ray rocking curv e full width at half maximum (FWHM) and dislocation density. Furthermore, i t was found that the higher the dislocation density, the higher the hole co ncentration. Therefore! we suggest that dislocations could act as a migrati on path or a neutralizing source for dissociated hydrogen impurities.