Characteristics of free-standing hydride-vapor-phase-epitaxy-grown GaN with very low defect concentration

A free-standing 300-μm-thick GaN template grown by hydride vapor phase epitaxy has been characterized for its structural and optical properties using x-ray diffraction, defect delineation etch followed by imaging with atomic force microscopy, and variable temperature photoluminescence. The Ga face and the N face of the c-plane GaN exhibited a wide variation in terms of the defect density. The defect concentrations on Ga and N faces were about 5×105 cm−2 for the former and about 1×107 cm−2 for the latter. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (10–14) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth as measured on the Ga and N faces (after a chemical etching to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.44 eV.