Optical properties of Yb ions in GaN epilayer

In recent years, an important effort in semiconductor materials research has been devoted to III-nitrides semiconductors doped with rare earth ions due to the high potential of these materials in light-emitting device applications. Ytterbium (Yb ³⁺ ) is one of a few lanthanide ions which have not been investigated as an optically active center in these materials yet. In this paper we report the observation of luminescence from GaN films grown on sapphire (0 0 0 1) substrate by metal organic chemical vapor deposition and doped by implantation with Yb ³⁺ ions. The high resolution photo- and cathodoluminescence spectra of GaN:Yb ³⁺ were studied at different excitation conditions in temperatures ranging from 8 to 330 K and revealed weak thermal quenching. The luminescence emission lines are assigned to transitions between the spin-orbit levels ²F _5/2 → ²F _7/2 of Yb ³⁺ (4f ¹³ ). The analysis of the Yb luminescence spectra allowed us to suggest the energy level diagram of the crystal-field-split 4f ¹³ levels for the Yb ion center. The most probable lattice location of Yb in GaN is the substitutional Ga site. Furthermore, the luminescence kinetics of internal transitions of Yb ³⁺ incorporated in GaN was investigated by means of decay and time-resolved luminescence measurements. It was found that the ytterbium decay is non-exponential with dominant exponential term of ∼100 μs with little dependence on the ambient temperature. The results indicate that Yb-doped GaN epilayer may be suitable as a material for near infrared optoelectronic devices.