Voids And Vacancy-Type Defects In Sio2/Gan Structures Probed By Monoenergetic Positron Beams

Voids in SiO2 films deposited on GaN were probed by using monoenergetic positron beams. The films were fabricated on GaN substrates by using plasma-enhanced chemical vapor deposition. The size and density of the voids in the films increased up to an annealing temperature of 800 degrees C and then decreased at 1000 degrees C. The observed annealing behaviors of the voids were attributed to the desorption of impurities incorporated during the deposition process and the shrinkage of the Si-O matrix by high-temperature annealing. Vacancy-type defects were introduced into the GaN substrate after 1000 degrees C annealing in O-2 atmosphere due to the diffusion of Ga from the substrate to the SiO2 film. No out-diffusion of Ga into the SiO2 film was observed for the annealing in N-2 atmosphere. Thus, the observed out-diffusion of Ga was attributed to the enhanced oxidation of GaN during the annealing in O-2 atmosphere. The diffusion of positrons implanted into the GaN substrate toward the SiO2 film was suppressed by annealing, suggesting a decrease in the negative charges in the SiO2 film or near the SiO2/GaN interface.