Study of absorption spectra of Er3+ ions in GaN crystals

The f-f absorption spectra of Er3 introduced by diffusion into bulk GaN crystals grown by vapour-phase epitaxy in a chloride system have been studied. The wavelength interval of 518-527 nm corresponding to the region of 4I15/2 RT 2H11/2 transitions has been studied in detail at 293, 77, and 2 K. At T= 2 K the 4I15/2 RT 2H11/2 spectrum contains six lines in accordance with theoretical predictions for Er3 in a noncubic crystal field. The positions of levels in the 2H11/2 multiplet correspond to 2.360, 2.361, 2.365, 2.369, 2.379, and 2.386 eV. Both the number and narrow width of lines observed at T= 2 K indicate that in our samples Er3+ ions occupy predominantly the same regular position in GaN crystals. Most probably, Er3+ ions substitute Ga atoms in the crystal lattice.