Study of optical properties of bulk GaN crystals grown by HVPE

•The investigated samples were sliced from the same bulk crystal.•No correlation between the O or C impurities and the weak YL band is observed.•A well-regulated relationship between the YL band and the dislocations is found.•A competition between the TES-Si lines and the YL band is discussed.•The dislocations trapping Si impurity is suggested to be responsible for YL band.

We investigated the optical properties of a series of GaN samples sliced from the same bulk crystal grown using hydride vapor phase epitaxy. The high crystalline quality of the samples was evaluated using cathodoluminescence measurements, and the dislocation density ranged from 2.4 × 106 to 2.3 × 105 cm−2. The impurity concentration was determined using secondary-ion mass spectroscopy, and photoluminescence (PL) measurements were conducted in the range of 3–300 K. We did not find a correlation between the O or C impurities and the weak yellow luminescence (YL) band. As the dislocation density decreased, the intensity of the band edge emission increased and that of the YL band decreased. A competition between the two-electron satellite lines correlated to Si and the YL band was also observed in the low-temperature PL spectra, which demonstrated that the Si impurity also plays an important role in the weak YL band of these GaN samples. These results indicate that the Si donors around the dislocations, as reasonable sources of shallow donors, will recombine with possible deep acceptors and finally respond with the YL.