High defect concentration in GaN:Gd layers grown by reactive molecular beam epitaxy

Using X-ray diffraction, photoconductivity and temperature dependent conductivity measurements, we investigate GaN:Gd layers grown by reactive molecular-beam epitaxy with the Gd concentration ranging from 7×1015 to 8.5×1018 cm−3. Our study reveals that the incorporation of Gd produces a large concentration of defects in the GaN lattice. The density of these defects generated even with a Gd concentration as low as 7×1015 cm−3 is estimated to be as high as ≈1019 cm−3. The defect state is found to be located ≈450 meV away from the band edge.