DEFECT STRUCTURE IN SELECTIVELY GROWN GAN FILMS WITH LOW THREADING DISLOCATION DENSITY

We have characterized by transmission electron microscopy (TEM) defect structures in GaN films grown selectively in hydride vapor-phase epit axy (HVPE). In this experiment, growth was achieved on SiO2-stripe-pat terned GaN layers that had been grown by metalorganic vapor-phase epit axy (MOVPE) on sapphire substrates. Cross-sectional TEM revealed unamb iguously that most of the dislocations, which originated from threadin g dislocations vertically aligned in the MOVPE-grown layer, propagated laterally around the SiO2 mask in the HVPE-grown film before the film thickness amounted to about 5 mu m. This change of the propagation di rection prevented the dislocations from crossing the film to the surfa ce region and thus principally led to a drastic reduction in the threa ding dislocation density in thicker films. (C) 1997 American Institute of Physics.