The X-ray topography results correlated with chemical etching of as grown pure and doped GCOB single crystals show various crystal lattice defects related to anomalies observed in optical measurements. Straight and curved dislocations, spherical inclusions were observed. The etch pits were found mainly at the outer part of the crystal along [010] direction with maximum content of 1.8 × 104 cm2. The broad and strong bands of UV absorption edge spectra and the inhomogeneous broadening of emission lines are presented and are explained by the defect structure.

Keywords: doped-GCOB crystal, defects, optical properties