A quantitative electron paramagnetic resonance study was made of V-related defects in semi-insulating and co-doped p-type and n-type V-doped samples. The results showed that the VCd donor was the predominant electrically and optically active defect in semi-insulating photo-refractive material. The effective trap density of 4 x 1015/cm3 of the VCd0/+ defect, as determined by means of quantitative electron paramagnetic resonance spectroscopy,  agreed with values which were deduced from photo-refractive measurements of the same crystals. A comparison of the total V content with the VCd donor concentration indicated the existence of additional V-related defects which were not detected in electron paramagnetic resonance data. The neutral donor state, VCd0, was not detected by electron paramagnetic resonance studies of n-type material. No other V-related defects were detected in n-type or p-type samples.

H.J.Von Bardeleben, V.Mazoyer, X.Launay, J.C.Launay: Semiconductor Science and Technology, 1995, 10[2], 163-6