Yellow and green luminescence in a freestanding GaN template

We have studied a broad photoluminescence band in high-mobility freestandin g 200-mum-thick GaN template prepared by hydride vapor-phase epitaxy. Varia ble-excitation intensity and energy experiments showed two defect-related b ands: a yellow luminescence (YL) band at about 2.15 eV and a green luminesc ence (GL) band at about 2.43 eV. In contrast to epitaxial GaN samples prepa red by both vapor-phase and molecular-beam epitaxy, the YL in the sample st udied is weak and can be easily saturated. However, the GL is dominant. We attribute the GL to isolated defects involving gallium vacancies and the YL to the same defect, but bound to dislocations, or possibly to structural s urface defects. (C) 2001 American Institute of Physics.