Point Defects in GaN

In this chapter, a critical analysis of point defects in GaN and their manifestation in such experiments as photoluminescence (PL), deep-level transient spectroscopy (DLTS), positron annihilation spectroscopy (PAS) is presented. Only a few PL bands are attributed to specific defects. The dominant defect-related PL band in GaN grown by metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy is the yellow luminescence (YL) band with a maximum at 2.2 eV, which is attributed to the CNON complex. In DLTS studies, it is known as a hole trap H1 with the ionization energy of about 0.85 eV. In thick GaN layers grown by hydride vapor phase epitaxy (HVPE) or in bulk GaN grown by some other techniques, the green luminescence (GL) band with a maximum at 2.4 eV is the dominant PL band. The GL band and the YL band in these samples are attributed to two charge states of the CN defect. The blue luminescence band with a maximum at 2.9 eV in undoped and Zn-doped GaN grown by HVPE or MOCVD is attributed to the ZnGa acceptor. The GL2 band observed in high-resistivity GaN samples at 2.35 eV is caused by an internal transition at the VN defect. The VGaON defect is present with high concentrations in n-type GaN and can be detected by PAS and optical DLTS. Most likely, it is a nonradiative defect and cannot be detected by PL.