Native and process induced defects in GaN films grown on Si substrates probed using a monoenergetic positron beam

Positron annihilation is a non-destructive tool for investigating vacancy-type defects in materials. Detectable defects are monovacancies to vacancy clusters, and there is no restriction onsample temperature or conductivity. Using this technique, we studied native and plasma-treatment induced defects in GaN layers grown on Si substrates deposited by metal organic chemical vapor deposition. Measurements of Doppler broadening spectra of the annihilation radiation for 1-μm-thick GaN layers showed that optically active vacancy-type defects were formed during their growth. These defects were identified as complexes of vacancies and carbon impurities. For plasma treated samples, we found the introduction of vacancy-type defects in the subsurface region (≤2.5 nm). These results show that positron annihilation spectroscopy is a useful tool for identifying vacancy-type defects in GaN-based devices.